Fluorocarbon emulsion stabilizing surfactants

ABSTRACT

Surfactants (e.g., fluorosurfactants) for stabilizing aqueous or hydrocarbon droplets in a fluorophilic continuous phase are presented. In some embodiments, fluorosurfactants include a fluorophilic tail soluble in a fluorophilic (e.g., fluorocarbon) continuous phase, and a headgroup soluble in either an aqueous phase or a lipophilic (e.g., hydrocarbon) phase. The combination of a fluorophilic tail and a headgroup may be chosen so as to create a surfactant with a suitable geometry for forming stabilized reverse emulsion droplets having a disperse aqueous or lipophilic phase in a continuous, fluorophilic phase. In some embodiments, the headgroup is preferably non-ionic and can prevent or limit the adsorption of molecules at the interface between the surfactant and the discontinuous phase. This configuration can allow the droplet to serve, for example, as a reaction site for certain chemical and/or biological reactions. In another embodiment, aqueous droplets are stabilized in a fluorocarbon phase at least in part by the electrostatic attraction of two oppositely charged or polar components, one of which is at least partially soluble in the dispersed phase, the other at least partially soluble in the continuous phase. One component may provide colloidal stability of the emulsion, and the other may prevent the adsorption of biomolecules at the interface between a component and the discontinuous phase. Advantageously, surfactants and surfactant combinations of the invention may provide sufficient stabilization against coalescence of droplets, without interfering with processes that can be carried out inside the droplets.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/310,048, filed Feb. 9, 2009, which is a 35 U.S.C. §371 National PhaseApplication of PCT/US2007/017617, filed Aug. 7, 2007, which claimspriority to, and the benefit of, U.S. Provisional Patent Application No.60/836,455, filed Aug. 7, 2006. Each of these applications isincorporated herein by reference in its entirety.

FIELD OF INVENTION

The present invention relates generally to surfactants, and morespecifically, to surfactants for stabilizing emulsions having acontinuous fluorophilic phase.

BACKGROUND

Many emulsions comprise an aqueous phase and a hydrocarbon oil phase.Fluorocarbon oils are often immiscible with both water and hydrocarbonoils; thus, water or hydrocarbon oils may be dispersed as emulsiondroplets in a fluorocarbon phase. The use of fluorocarbon oils as thecontinuous phase of an emulsion offers advantages over conventionalhydrocarbon systems. For example, fluorocarbon oils may be well suitedas the continuous phase for emulsions that require reduced diffusionand/or cross-contamination of hydrophilic or lipophilic material betweendroplets in the emulsion. Stabilizing such emulsions, however, sometimesrequires the addition of appropriate surfactants, and these surfactantsare often not available or do not have desirable physicalcharacteristics. This is especially true because fluorocarbons are notcommonly used as the continuous emulsion phase. Accordingly, newsurfactants and surfactant systems for stabilizing droplets of water andhydrocarbon oils or organic solvents in a continuous fluorophilic phaseare needed.

SUMMARY OF THE INVENTION

Surfactants for stabilizing emulsions having a continuous fluorophilicphase are presented. In one embodiment, a fluorosurfactant is provided.The fluorosurfactant has one of the general formulas: A-B-A or A-B or(A-B)_(n) or B-(A)_(n), or (B)_(n)-A or A-B-A′, where A (and A′, ifpresent) comprises a fluorophilic component having a molecular weightgreater than 1,000 or greater than 1,500 g/mol, the fluorophiliccomponent comprising a (per)fluoropolyether or a differentpoly(perfluoroalkyl-methacrylates), etc., and B is one or both of: a)non-ionic and soluble in an aqueous phase; or b) a hydrocarbon solublein a hydrocarbon phase, and n is an integer greater than 0. In otherembodiments, the fluorosurfactant may have a formula such as thosedescribed herein.

In another embodiment, a macroemulsion is provided. The macroemulsioncomprises an aqueous dispersed phase or a lipophilic dispersed phasehaving an average diameter greater than or equal to about 50 nanometers,a continuous phase comprising a fluorinated solvent or oil, and afluorinated, non-ionic surfactant, where at least 95% of the dispersedphase does not coalesce for at least 30 minutes at 25 degrees C. and 1atm.

In one aspect, the invention is directed to an article. In one set ofembodiments, the article comprises a fluorosurfactant comprising theformula: A-B-A or A-B or (A-B)_(n) or B-(A)_(n) or (B)_(n)-A or A-B-A′or A-X—B or A-X¹—B—X²-A or (A-X¹—B—X²)_(n) or B—X-(A)_(n) or B—(X-A)_(n)or B-(A-X)_(n) or B—X¹-(A-X²)_(n), wherein A and A′ comprise afluorophilic component having a molecular weight greater than 1,000g/mol, the fluorophilic component comprises a fluoropolyether; B iseither: a) non-ionic and soluble in an aqueous phase or b) a hydrocarbonsoluble in a hydrocarbon phase; X, when present, is either a covalentbond or a linking group, and X¹ and X², where present, may be the sameor different; and n is an integer greater than 0.

In another set of embodiments, the fluorosurfactant comprises theformula: A-B-A or A-B or (A-B—)_(n) or B-(A)_(n) or (B)_(n)-A or A-B-A′or A-X—B or A-X¹—B—X²-A or (A-X¹—B—X²)_(n) or B—X-(A)_(n) or B—(X-A)_(n)or B-(A-X)_(n) or B—X¹-(A-X²)_(n), wherein A and A′ comprise a componenthaving a molecular weight greater than 1,000 g/mol, the componentcomprising a fluorophilic portion having fluorinated side chains; B iseither: a) non-ionic and soluble in an aqueous phase or b) a hydrocarbonsoluble in a hydrocarbon phase; X, when present, is either a covalentbond or a linking group, and X¹ and X², where present, may be the sameor different; and n is an integer greater than 0.

In still another set of embodiments, the fluorosurfactant comprises theformula: A-B-A or A-B or (A-B—)_(n) or B-(A)_(n) or (B)_(n)-A or A-B-A′or A-X—B or A-X¹—B—X²-A or (A-X¹—B—X²)_(n) or B—X-(A)_(n) or B—(X-A)_(n)or B-(A-X)_(n) or B—X¹-(A-X²)_(n), wherein A and A′ comprise a componenthaving a molecular weight greater than 1,000 g/mol; B is either: a)non-ionic and soluble in an aqueous phase or b) a hydrocarbon soluble ina hydrocarbon phase; X, when present, is either a covalent bond or alinking group, and X¹ and X², where present, may be the same ordifferent; and n is an integer greater than 0.

In yet another set of embodiments, the fluorosurfactant has a backbonecomprising the formula: A-B-A or A-B or (A-B—)_(n) or B-(A)_(n) or(B)_(n)-A or A-B-A′ or A-X—B or A-X¹—B—X²-A or (A-X¹—B—X²)_(n) orB—X-(A)_(n) or B—(X-A)_(n) or B-(A-X)_(n) or B—X¹-(A-X²)_(n), wherein Aand A′ comprise a fluorophilic component having a molecular weightgreater than 1,000 g/mol, the fluorophilic component comprising afluoropolyether; B is either: a) non-ionic and soluble in an aqueousphase or b) a hydrocarbon soluble in a hydrocarbon phase; X, whenpresent, is either a covalent bond or a linking group, and X¹ and X²,where present, may be the same or different; and n is an integer greaterthan 0.

In another set of embodiments, the fluorosurfactant having a backbonecomprising the formula: A-B-A or A-B or (A-B—)_(n) or B-(A)_(n) or(B)_(n)-A or A-B-A′ or A-X—B or A-X¹—B—X²-A or (A-X¹—B—X²)_(n) orB—X-(A)_(n) or B—(X-A)_(n) or B-(A-X)_(n) or B—X¹-(A-X²)_(n), wherein Aand A′ comprise a fluorophilic component comprising a(per)fluoropolyether; B is either: a) non-ionic and soluble in anaqueous phase or b) a hydrocarbon soluble in a hydrocarbon phase; X,when present, is either a covalent bond or a linking group, and X¹ andX², where present, may be the same or different; and n is an integergreater than 0.

In another aspect, the invention is directed to an emulsion. In one setof embodiments, the emulsion comprises an aqueous, polar, and/orhydrophilic dispersed phase or a lipophilic dispersed phase having anaverage diameter greater than or equal to about 50 nm; a continuousphase comprising a fluorinated solvent or oil; and a fluorinated,non-ionic surfactant. In some cases, at least 95% of the dispersed phasedoes not coalesce for at least 30 minutes at 25 degrees C. and 1 atm.

In another set of embodiments, the emulsion comprises an aqueousdispersed phase or a lipophilic dispersed phase having an averagediameter greater than or equal to about 50 nm; a continuous phasecomprising a fluorinated solvent or oil; and a fluorinated surfactantcomprising a morpholino group. The emulsion, in still another set ofembodiments, includes an aqueous dispersed phase or a lipophilicdispersed phase having an average diameter greater than or equal toabout 50 nm; a continuous phase comprising a fluorinated solvent or oil;and a fluorinated surfactant comprising a phosphate group.

Yet another embodiment is directed to a method. The method, in one somecases, is generally directed to performing a chemical and/or biologicalreaction it he dispersed phase of any of the embodiments describedabove, or described herein.

In another aspect, the present invention is directed to a method ofmaking one or more of the embodiments described herein. In anotheraspect, the present invention is directed to a method of using one ormore of the embodiments described herein.

Other advantages and novel features of the present invention will becomeapparent from the following detailed description of various non-limitingembodiments of the invention when considered in conjunction with theaccompanying figures. In cases where the present specification and adocument incorporated by reference include conflicting and/orinconsistent disclosure, the present specification shall control. If twoor more documents incorporated by reference include conflicting and/orinconsistent disclosure with respect to each other, then the documenthaving the later effective date shall control.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present invention will be described byway of example with reference to the accompanying figures, which areschematic and are not intended to be drawn to scale. In the figures,each identical or nearly identical component illustrated is typicallyrepresented by a single numeral. For purposes of clarity, not everycomponent is labeled in every figure, nor is every component of eachembodiment of the invention shown where illustration is not necessary toallow those of ordinary skill in the art to understand the invention. Inthe figures:

FIG. 1A shows an aqueous droplet containing a non-adsorbed biologicaland/or chemical species therein, of an aqueous-in-fluorophilic emulsion,according to one embodiment of the invention;

FIG. 1B shows an aqueous droplet containing an adsorbed biologicaland/or chemical species therein, of an aqueous-in-fluorophilic emulsion,according to one embodiment of the invention;

FIG. 2A shows the combination of a headgroup and a fluorophilic tail toform a diblock surfactant according to one embodiment of the invention;

FIG. 2B shows the combination of a headgroup and two fluorophilic tailsto form triblock surfactant according to one embodiment of theinvention;

FIG. 2C shows the combination of a headgroup with three fluorophilictails to form a multi-block surfactant according to one embodiment ofthe invention;

FIGS. 2D-2G show various fluorosurfactants including linking moitiesaccording to embodiments of the invention;

FIGS. 3A-3D show various non-limiting illustrative geometries ofsurfactants according to one embodiment of the invention;

FIG. 3E shows a non-limiting example of packing geometry of surfactantsto form a droplet of an emulsion according to one embodiment of theinvention;

FIG. 4 shows a schematic diagram illustrating adsorption and desorptionof fluorosurfactants during emulsification according to one embodimentof the invention;

FIG. 5 shows a schematic diagram illustrating steric stabilization ofdroplets against coalescence according to one embodiment of theinvention;

FIG. 6 shows a non-limiting example of a device used to form an emulsionaccording to one embodiment of the invention;

FIG. 7 shows in-vitro translation inside droplets of an emulsionaccording to one embodiment of the invention;

FIGS. 8A and 8B are bright-field and fluorescent micrographs,respectively, showing fluorescein-labelled polyurethane particles formedby suspension polymerization according to one embodiment of theinvention;

FIG. 9A is a micrograph showing a monodisperse precursor emulsion in afluorophilic continuous phase according to one embodiment of theinvention;

FIG. 9B is a micrograph showing dried monodisperse polyurethane latexparticles according to one embodiment of the invention;

FIGS. 10A and 10B are bright-field and fluorescent micrographs,respectively, showing dried, fluorescently labeled, monodisperseparticles of polyurethane latex according to one embodiment of theinvention;

FIGS. 11A and 11B are bright-field and fluorescent micrographs,respectively, showing cross-linked and fluorescently labeledpolyurethane latex particles formed by suspension polymerization in asingle process step according to one embodiment of the invention;

FIGS. 12A and 12B show cross-linked PU-particles, whose precursor wasdiluted with an equal volume of DMSO prior to emulsification accordingto one embodiment of the invention;

FIGS. 13A and 13B show reinjection and collection of aqueous dropletsinto a microfluidic device according to one embodiment of the invention;

FIG. 14 illustrates the formation of droplets by hydrodynamic flowfocusing and the stability of the droplets immediately afteremulsification according to one embodiment of the invention;

FIG. 15 shows monodisperse droplets formed in microfluidic devicescontaining viable yeast cells according to one embodiment of theinvention;

FIGS. 16A-16C illustrate NMR spectra of certain compounds of theinvention;

FIGS. 17A-17H illustrate cells exposed to various surfactants of theinvention;

FIG. 18 illustrates the expression of genes in cells exposed to asurfactant, in accordance with one embodiment of the invention; and

FIG. 19 illustrates an enzymatic reaction, in accordance with anotherembodiment of the invention.

DETAILED DESCRIPTION

Surfactants (e.g., fluorosurfactants) for stabilizing aqueous orhydrocarbon droplets in a fluorophilic continuous phase are presented(or vice versa). In some embodiments, the fluorosurfactants include afluorophilic tail soluble in a fluorophilic (e.g., fluorocarbon)continuous phase, and a headgroup soluble in either an aqueous phase ora lipophilic (e.g., hydrocarbon) phase. The headgroup and the tail maybe directly linked, or linked via a linking moiety. The combination of afluorophilic tail and a headgroup may be chosen so as to create asurfactant with a suitable geometry for forming stabilized reverseemulsion droplets having a disperse aqueous or lipophilic phase in acontinuous, fluorophilic phase. In some embodiments, the headgroup isnon-ionic and can prevent or limit the adsorption of molecules at theinterface between the surfactant and the discontinuous phase. Thisconfiguration can allow the droplet to serve, for example, as a reactionsite for certain chemical and/or biological reactions. In anotherembodiment, aqueous droplets are stabilized in a fluorocarbon phase atleast in part by the electrostatic attraction of two oppositely chargedor polar components, one of which is at least partially soluble in thedispersed phase, the other at least partially soluble in the continuousphase. One component may provide colloidal stability of the emulsion,and the other may prevent the adsorption of biomolecules at theinterface between a component and the discontinuous phase.Advantageously, surfactants and surfactant combinations of the inventionmay provide sufficient stabilization against coalescence of droplets incertain embodiments of the invention, without interfering with processesthat can be carried out inside the droplets.

An “emulsion,” as used herein, is a stable mixture of at least twoimmiscible liquids. In general, immiscible liquids tend to separate intotwo distinct phases. An emulsion is thus stabilized by the addition of a“surfactant” which functions to reduce surface tension between the atleast two immiscible liquids and/or to stabilize the interface. In someembodiments, emulsion described herein include a discontinuous ordisperse phase (i.e., the isolated phase stabilized by a surfactant)formed of an aqueous or lipophilic (e.g., hydrocarbon) substance. Thecontinuous phase may be formed of a fluorophilic substance (e.g., afluorocarbon). The present invention involves, in some embodiments,water-in-fluorocarbon emulsions and hydrocarbon-in-fluorocarbonemulsions having a disperse aqueous or hydrocarbon phase and afluorocarbon continuous phase. The isolated disperse aqueous orlipophilic phase in a fluorophilic solvent can form a “reverseemulsion,” which is simply one example of an emulsion. In someparticular embodiments, the emulsions described herein aremacroemulsions. Macroemulsions are emulsions that are kineticallystable, as compared to microemulsions, which are thermodynamicallystable and undergo spontaneous formation. In some cases, a microemulsionmay include droplets having an average diameter of less than about 50nm.

As used herein “droplet” means an isolated aqueous or lipophilic phasewithin a continuous phase having any shape, for example cylindrical,spherical, ellipsoidal, irregular shapes, etc. Generally, in emulsionsof the invention, aqueous and/or lipophilic droplets are spherical orsubstantially spherical in a fluorocarbon, continuous phase.

As used herein, “surfactant” defines a molecule that, when combined witha first component defining a first phase, and a second componentdefining a second phase, will facilitate assembly of separate first andsecond phases. In some cases, a surfactant of the invention typicallycan have one or more main fluorophilic chain(s) where one end of thechain is soluble in the fluorophilic phase of the emulsion and one ormore chains that are not soluble in the fluorophilic phase of theemulsion (e.g., those chains may be soluble in the aqueous or lipophilicphase). For instance, a surfactant may be a multi-block surfactant(e.g., ABABABA . . . ), where one component of the chain (e.g., “A”) issoluble in the fluorophilic phase and another component of the chain(e.g., “B”) is soluble in the other phase (e.g., the aqueous orlipophilic phase). As used herein, a multi-block surfactant is asurfactant having an alternating copolymeric structure or an (A-B—)_(n)structure, i.e., ABA, ABAB, ABABA, ABABABA, etc.). In some cases, oneblock may be soluble in the fluorophilic phase of the emulsion and oneblock may be soluble in the other phase of the emulsion (e.g., theaqueous or lipophilic phase). In still other cases, additionalcomponents may be present within the surfactant. For example, amulti-block surfactant may have other groups present within itspolymeric structure, for example, linking moieties connecting A and B,e.g., (A-X—B—)_(n), (A-B—X)_(n), (A-X¹—B—X²)_(n), or the like, where “X”represents a covalent bond or a linking moiety, as described below, andX¹ and X², where present, may be the same or different.

As used herein, a “fluorophilic” component comprises any fluorinatedcompound such as a linear, branched, cyclic, saturated, or unsaturatedfluorinated hydrocarbon. The fluorophilic, component can optionallyinclude at least one heteroatom (e.g., in the backbone of thecomponent). In some cases, the fluorophilic compound may be highlyfluorinated, i.e., at least 30%, at least 50%, at least 70%, or at least90% of the hydrogen atoms of the component are replaced by fluorineatoms. The fluorophilic component may comprise a fluorine to hydrogenratio of, for example, at least 0.2:1, at least 0.5:1, at least 1:1, atleast 2:1, at least 5:1, or at least 10:1. In some such embodiments, atleast 30%, at least 50%, at least 70%, or at least 90% but less than100% of the hydrogen atoms of the component are replaced by fluorineatoms. In other cases, the fluorophilic component is perfluorinated,i.e., the component contains fluorine atoms but contains no hydrogenatoms. Fluorophilic components compatible with the present invention mayhave low toxicity, low surface tension, and the ability to dissolve andtransport gases. Examples of fluorophilic components are describedbelow.

As mentioned, in some embodiments, the emulsions of the inventioninclude discontinuous aqueous and/or lipophilic (e.g., hydrocarbon)droplets in a continuous, fluorophilic phase. This means that separate,isolated regions of droplets of an aqueous and/or lipophilic componentare contained within a continuous fluorophilic phase, which may bedefined by a fluorocarbon component. The discontinuous aqueous and/orlipophilic droplets in the nonaqueous phase typically have an averagecross-sectional dimension of greater than 25 nm. In some embodiments,the average cross-sectional dimension of the droplets is greater than 50nm, greater than 100 nm, greater than 250 nm, greater than 500 nm,greater than 1 micron, greater than 5 microns, greater than 10 microns,greater than 50 microns, greater than 100 microns, greater than 200microns, or greater than 500 microns, etc. As used herein, the averagecross-sectional dimension of a droplet is the diameter of a perfectsphere having the same volume as the droplet.

Compositions of the invention are, according to some embodiments, stablefor at least about 1 minute, at least about 5 minutes, at least about 10minutes, at least about 20 minutes, at least about 30 minutes, at leastabout 40 minutes, at least about 1 hour, at least about 2 hours, atleast about 6 hours, at least about 12 hours, at least about 1 day, atleast about 1 week, at least about 1 month, or at least about 2 months,at a temperature of about 25 degrees Celsius and a pressure of 1 atm. Asused herein, a “stable emulsion” means that at least about 95% of thedroplets of the emulsion do not coalesce, e.g., to form larger dropletsover these periods of time.

As used herein, “nonaqueous” is meant to define material such as a fluidthat is immiscible with water. That is, a liquid that when mixed withwater will form a stable two-phase mixture. The non-aqueous phase neednot be liquid, but can be a solid or semi-solid lipid or other nonpolarsubstance that is not soluble in water. In some instances, thenonaqueous phase can include a lipophilic component (e.g., ahydrocarbon) or a fluorinated component (e.g., a fluorocarbon). Theaqueous phase can be any liquid miscible with water; that is, any liquidthat, when admixed with water, can form a room-temperature, single-phasesolution that is stable. In some cases, the aqueous phase can compriseone or more physiologically acceptable reagents and/or solvents, etc.Non-limiting examples of aqueous phase materials include (besides wateritself) methanol, ethanol, DMF (dimethylformamide), or DMSO (dimethylsulfoxide).

Referring now to FIG. 1A, as a non-limiting illustration, anaqueous-in-fluorophilic (aqueous-in-fluorocarbon) emulsion 5 is shown.The emulsion includes a droplet 10 comprising an aqueous discontinuousphase 20, a fluorophilic (e.g., fluorocarbon) continuous phase 30, andsurfactant molecules 40 at the interface. The surfactant moleculesinclude tail 42 and headgroup 44. Typically, the tail is a fluorophilicchain soluble in the fluorophilic phase of the emulsion and theheadgroup is soluble in the discontinuous phase. In this particularnon-limiting embodiment, the headgroup is a hydrophilic componentsoluble in the aqueous discontinuous phase. The headgroup may benon-ionic in certain embodiments. In other embodiments involvinghydrocarbon-in-fluorocarbon emulsions, the headgroup is a lipophiliccomponent soluble in a lipophilic (e.g., hydrocarbon) discontinuousphase.

Also shown in the embodiment illustrated in FIG. 1A are components 60and 62, such as proteins, DNA, and/or cells, which may be containedwithin the droplet. In some cases, components 60 and 62 aredistinguishable. The components may be, for example, reagents, analytes,reactants, etc. to be tested, assayed, and/or reacted within thedroplet. In embodiments in which headgroups 44 of the surfactants arenon-ionic, adsorption of the components onto the interface between thesurfactant and the discontinuous phase may be limited or prevented insome, but not all, cases. Advantageously, this passivation of theinterface may allow the components to be investigated as if they werefloating in a bulk medium in certain embodiments of the invention, asdescribed in more detail below. In contrast, FIG. 1B shows components 60and 62 adsorbed onto the interface between the surfactant and thediscontinuous phase of the droplet, according to another embodiment ofthe invention. This adsorption may occur, in some cases, when theheadgroup is ionic and/or includes a chemical moiety that preferentiallybinds and/or adsorbs the components.

FIGS. 2A-2C show various non-limiting embodiments of fluorosurfactantsof the invention. As shown in the illustrative embodiment of FIG. 2A,fluorosurfactant 80 includes headgroup 82 and fluorophilic component 84.As used herein, a fluorophilic component such as component 84 isreferred to as an “A”-block and a non-fluorophilic component of asurfactant, e.g., headgroup 82, is referred to as a “B”-block. Thecombination of a headgroup with a single fluorophilic component forms an“A-B” structure. The A-B structure is referred to as a diblockstructure. In some embodiments of the invention, fluorosurfactantsinclude a multi-block structure, for example, as shown in FIGS. 2B and2C. FIG. 2B shows the combination of a headgroup with two fluorophiliccomponents to form a triblock A-B-A structure 86. Structures such asA-B-A′, where A and A′ comprise different fluorophilic components, arealso possible. Additional fluorophilic components may be combined with aheadgroup to form other multi-block structures, e.g., as shown in FIG.2C. In some such embodiments, headgroup 82 may be a hydrophiliccomponent that is soluble in an aqueous phase. For example, in someparticular embodiments, headgroup 82 may be a non-ionic hydrophiliccomponent, such as a polyether. In other instances, headgroup 82 may bea lipophilic component soluble in a lipophilic (e.g., hydrocarbon)phase. Such an embodiment would be useful for forminghydrocarbon-in-fluorocarbon type emulsions. In addition, in some cases,other types of blocks (e.g., having other physical and/or chemicalproperties) may be included in the multi-block structure, and/or theblocks themselves may each independently have the same or differentnumbers of repeat units or monomers. For instance, in certain cases, afluorosurfactant of the invention may comprise random copolymers,terpolymers, and the like.

In another embodiment, a fluorosurfactant of the invention includes alinking moiety (which can be referred to as “X”), which may behydrophilic or hydrophobic, etc. As shown in FIG. 2D, a moiety 85 may bepositioned between the A and B components, e.g., between headgroup 82and fluorophilic component 84, to produce fluorosurfactant 89. In otherembodiments, a linking moiety 85 may be positioned between twoheadgroups, as illustrated in FIG. 2E. FIG. 2F shows a linking moiety 85attached to two headgroups and a fluorophilic component, and FIG. 2Gshows a linking moiety attached to two fluorophilic components and aheadgroups. Of course, other configurations are also possible. Linkingmoieties are described in more detail below.

One aspect of the invention involves the formation of stabilizedemulsions using fluorosurfactants including those described herein.Surprisingly, in order to obtain long-term stabilized emulsions, certaingeometries of the fluorosurfactants are needed in some cases. Forinstance, certain ratios of molecular weights of the fluorophiliccomponent to the headgroup component may be required for stericstabilization of the droplets. In addition, fluorophilic componentshaving large molecular weights can contribute to long term colloidalstabilization, according to certain embodiments. These and otherconsiderations for choosing appropriate components of fluorosurfactantsand suitable mixtures of fluorsurfactants may be suitable for formingcertain emulsions, for instance, emulsions comprising droplets having anaverage diameter in the micron or micrometer range. These and othercriteria are described in more detail below.

FIGS. 3A-3E show various non-limiting geometries and packing offluorosurfactants described herein useful for forming certain emulsionshaving a fluorophilic continuous phase. As illustrated in theseembodiments, fluorophilic components having different chemicalcompositions, molecular weights, and/or lengths can contribute to theoverall packing geometry of the surfactants (e.g., in the respectivefluorocarbon oil), and, therefore, to the stability of the droplets inthe macroemulsion.

The fluorophilic component of surfactant molecules described hereintypically comprise a fluorophilic chain at least C₈ in length (i.e.,contains at least 8 carbon atoms). In some embodiments, the fluorophilicchain is at least C₁₀ in length, at least C₁₅ in length, at least C₂₀ inlength, at least C₂₅ in length, or at least C₃₀ in length. In otherembodiments, the fluorophilic chain is at least C₅₀ in length, at leastC₇₅ in length, at least C₁₀₀ length, or greater. As a non-limitingexample, a fluorophilic component having the structure —(C₃F₆O)₁₀— has30 carbons equivalent to a C₃₀ chain. The fluorophilic component may belinear, branched, cyclic, saturated, unsaturated, etc.

In some embodiments, the fluorophilic component of a fluorosurfactantincludes a heteroatom (e.g., a non-carbon such as oxygen (e.g., divalentoxygen), sulfur (e.g., divalent or hexavalent sulfur), nitrogen (e.g.,trivalent nitrogen), etc.) in the structure of the component. Suchheteroatoms may be bonded, for example, to carbon atoms in the skeletalstructure of the component. Additionally and/or alternatively, thefluorophilic component may include one or more branches extending fromthe main chain of the structure.

In some embodiments, the fluorophilic component of a surfactant is afluorinated oligomer or polymer (i.e., a fluoropolymer). Thefluoropolymer may include a (per)fluoropolyether chain, among otherfluorinated polymers that are soluble in a fluorocarbon oil. The(per)fluoropolyether chain may comprise repeating units including, butnot limited to, —(C_(n)F_(2n)O)_(x)—, where n is an integer, forexample, —(C₃F₆O)_(x)—, —(C₄F₈O)_(x)—, —(C₅F₁₀O)_(x)—;—(CF(CF₃)CF₂O)_(n)—; —(CF₂CF₂O)_(x)—; —(CF(CF₃)CF₂O)_(x)—CF(CF₃)CONH—;—(CF₂(CF₂)_(z′)CF₂O)_(x)—, where z′ is an integer; —(CFLO)_(x)—, whereL=—F or —CF₃; and —(CH₂CF₂CF₂O)_(x)—. In some cases,(C_(n)F_(2n+1)O)_(x)—, where n is an integer (for example, —(CF₃O)_(x)—,—(C₂F₅O)_(x)—, —(C₃F₇O)_(x)—, etc.), is used as a terminal group and maynot be polymerizable. In some cases, the (per)fluoropolyether chain mayhave the structure (C_(n)F_(m)O)_(x)—, where n and m are integersproperly chosen to form a valid structure. In some embodiments, thefluoropolymer comprises poly((per)fluoromethylene oxide),poly((per)fluoroethylene oxide), poly((per)fluoropropylene oxide),and/or poly((per)fluorobutylene oxide). In one particular embodiment,the fluorophilic chain includes poly((per)fluoropropylene oxide). Inanother embodiment, the fluorophilic chain includes apoly((per)fluoroalkyl-methacrylate). Typically, x in the structuresabove is greater than or equal to 8. For example, x may be greater thanor equal to 10, greater than or equal to 14, greater than or equal to16, greater than or equal to 20, x greater than or equal to 30, greaterthan or equal to 40, or greater than or equal to 50.

Non-limiting examples of other types of fluorpolymers or oligomers thatcan be included in the fluorophilic chain, and/or as side chains,include vinylidene fluoride (VDF), (per)fluoroolefins (e.g.,tetrafluoroethylene (TFE)), chlorotrifluoroethylene (CTFE),(per)fluoroalkylvinylethers (PAVE), e.g., CF₂═CFOR_(f), where R_(f) is a(per)fluoroether or a C_(n) (per)fluoroalkyl such as trifluoromethyl orpentafluoropropyl, where n is an integer; andperfluoro-oxyalkylvinylethers CF₂═CFOR_(x), where x is a C₁-C₁₂perfluoro-oxyalkyl having one or more ether groups, for example,perfluoro-2-propoxy-propyl. Other examples of monomers present withinthe fluorophilic component include fluorinated acrylates and fluorinatedmethacrylates. In some cases, the fluorophilic component may be acomponent where at least about 10% or at least about 20% of the atomsdefining the component are fluorine atoms.

A fluorophilic component of a surfactant may have any suitable mixtureof hydrogen and fluorine atoms so long as the fluorophilic component issufficiently soluble in a suitable fluorophilic continuous phase. Thesolubility of a component in a fluorophilic continuous phase can bereadily determined by those of ordinary skill in the art using no morethan routine experimentation. For instance, a fluorophilic component maycomprise monomer units such as —(C₃F₅HO)_(x)—(C₃F₄H_(6-m)O)_(x)—,—(C₃F₄H₂O)_(x)—, etc. In some embodiments, the fluorophilic componenthas a ratio of fluorine to hydrogen atoms of greater than 1:1, greaterthan or equal to 3:1, greater than or equal to 5:1, greater than orequal to 6:1, greater than or equal to 9:1, greater than or equal to10:1, greater than or equal to 12:1, greater than or equal to 15:1, orgreater than or equal to 20:1. In certain embodiments, the fluorophiliccomponent is perfluorinated.

In some embodiments, the fluorophilic component of a surfactant includesone or more fluoropolymers, where the number of monomer units formingthe fluoropolymer is greater than or equal to 8. For example, thepolymer (or oligomer) may have greater than or equal to 5 monomers,greater than or equal to 10 monomers, greater than or equal to 14monomers, greater than or equal to 16 monomers, greater than or equal to20 monomers, greater than or equal to 30 monomers, greater than or equalto 40 monomers, or greater than or equal to 50 monomers, etc.

The fluorophilic component may have a molecular weight greater than orequal to 1,000 g/mol, greater than or equal to 1,200 g/mol, greater thanor equal to 1,500 g/mol, greater than or equal to 1,700 g/mol, greaterthan or equal to 1,900 g/mol, greater than or equal to 2,000 g/mol,greater than or equal to 2,200 g/mol, greater than or equal to 2,500g/mol, greater than or equal to 2,700 g/mol, greater than or equal to3,000 g/mol, greater than or equal to 3,200 g/mol, greater than or equalto 3,500 g/mol, greater than or equal to 3,700 g/mol, greater than orequal to 4,000 g/mol, greater than or equal to 4,200 g/mol, greater thanor equal to 4,500 g/mol, greater than or equal to 4,700 g/mol, greaterthan or equal to 5,000 g/mol, greater than or equal to 5,200 g/mol,greater than or equal to 5,500 g/mol, greater than or equal to 5,700g/mol, greater than or equal to 6,000 g/mol, greater than or equal to6,200 g/mol, greater than or equal to 6,500 g/mol, greater than or equalto 6,700 g/mol, greater than or equal to 7,000 g/mol, greater than orequal to 7,200 g/mol, greater than or equal to 7,500 g/mol, greater thanor equal to 7,700 g/mol, greater than or equal to 8,000 g/mol, greaterthan or equal to 8,200 g/mol, greater than or equal to 8,500 g/mol,greater than or equal to 8,700 g/mol, greater than or equal to 9,000g/mol, greater than or equal to 9,200 g/mol, greater than or equal to9,500 g/mol, greater than or equal to 9,700 g/mol, or greater than orequal to 10,000 g/mol.

The surfactants described herein may have a hydrophilic headgroup insome cases. In some embodiments, the hydrophilic component of asurfactant is a polymer (or oligomer). The polymer may include, forexample, a polyether. The polyether chain may comprise repeating unitsincluding, but not limited to, —(C_(n)H_(2n)O)_(x)—, where n is aninteger, for example, —(C₃H₆O)_(x)—, —(C₄H₈O)_(x)—, —(C₅H₁₀O)_(x)—;—(C₂H₄O)_(x)—(C₃H₆O)_(x)—, —(C₄H₈O)_(x)—,—(C₅H₁₀O)_(x)—(CH(CH₃)CH₂O)_(x)—; —(CH₂CH₂O)_(x)—;—(CH(CH₃)CH₂O)_(x)—CH(CH₃)CONH—; —(CH₂(CH₂)_(z′)CH₂O)_(x)—, where z′ isan integer; —(CHLO)_(x)—, where L=—H or —CH₃; or —(CH₂CH₂CH₂O)_(x)—. Thepolyether chain may include, in some cases, terminal groups such as(C_(n)H_(2n+1)O)_(x)—, where n is an integer, for example, (CH₃O)_(x)—,(C₂H₅O)_(x)—, (C₃H₇O)_(x)—, etc. In some embodiments, the hydrophiliccomponent comprises polymethylene oxide, polyethylene oxide,polybutylene oxide, and/or polyTHF, and/or various polymers thereof. Anon-limiting example is a JEFFAMINE® amine. In one particularembodiment, the fluorophilic chain includes polyethylene glycol.Typically, x in the hydrophilic structures above is greater than orequal to 1. For example, x may be greater than or equal to 5, greaterthan or equal to 10, greater than or equal to 14, greater than or equalto 16, greater than or equal to 20, greater than or equal to 30, greaterthan or equal to 40, or greater than or equal to 50. In otherembodiments, a headgroup can include a sugar (e.g., glucose,glucosamine, and sorbitol). Other polar headgroups known to those ofordinary skill in the art are also included within the scope of thepresent invention.

In one set of embodiments, a headgroup of a fluorosurfactant isconnected to a linking moiety. In some cases, the linking moiety is arelatively small entity. The linking entity may comprise, for example, amorpholino group (e.g., dimorpholino and monomoropholino groups). Thelinking entity also may comprises a phosphate group in some instances.In certain embodiments, the linking entity comprises both a morpholinogroup and a phosphate group (e.g., a dimoporpholino phosphate).

In some embodiments, a linking moiety (e.g., positioned between A and Bcomponents of a fluorosurfactant) may be chosen to assist the selfassembly and the packing of the fluorosurfactant at the interface.Additionally, a linking moiety may have a good impact on the CMC(critical micelle concentration), and therefore on the diffusion to anewly formed interface from the fluorophilic phase, which may beimportant for emulsification.

In one set of embodiments, the headgroups of the surfactants may bechosen to render the surfactant soluble in water and/or relativelybiologically inert. As mentioned, headgroups such as dimorpholinophosphate (DMP) and polyethylene glycol (PEG) are examples ofpotentially suitable headgroups. A non-limiting example of a tail of asurfactant is Krytox FS(H) (manufactured by DuPont), a carboxylicacid-terminated perfluoropolyether. This tail may have stability influorocarbon oils, its length (which can provide steric repulsionbetween the surfactant molecules), and the fact that it possesses aterminal group that is suitable for the grafting of differentheadgroups.

Specific examples of potentially suitable headgroups include, but arenot limited to:

Specific examples of potentially suitable tails include, but are notlimited to:

where x is any positive integer, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9,10, etc.

In some cases, a surfactant of the instant invention may also include alinking moiety. Non-limiting examples of linking moieties includecarbonyls (—C(O)—) and phosphates (PO₄). In some cases, the linkingmoiety may connect more than one headgroup and/or more than one tail.For instance, a phosphate linking moiety may connect two headgroups(which each may the same or different), two tails (which each may thesame or different) and a headgroup, etc.

Thus, in one set of embodiments, a surfactant of the present inventionmay include a headgroup (or more than one headgroup), a tail (or morethan one tail), and optionally, a linking moiety (or more than onemoiety), including the headgroups, tails, and linking moieties describedabove. Specific, non-limiting examples of some of the surfactants of theinvention, comprising a head group, a tail, and optionally a linkingmoiety, follow:

The hydrophilic component of a surfactant of the present invention mayhave any molecular weight suitable for forming a water-in-fluorocarbontype emulsion. For instance, the molecular weight of the hydrophiliccomponent may be greater than or equal to 100 g/mol, greater than orequal to 200 g/mol, greater than or equal to 300 g/mol, greater than orequal to 500 g/mol, greater than or equal to 800 g/mol, greater than orequal to 1,000 g/mol, greater than or equal to 1,500 g/mol, or greaterthan or equal to 2,000 g/mol, etc.

In some applications involving oil-in-fluorocarbon type emulsions and/orlipophilic solvent applications, a surfactant having a headgroupcomprising a lipophilic component may be desired. The lipophiliccomponent may include, for example, an alkyl block, —(CH₂)_(x)—. In someembodiments, x is less than or equal to 20, less than or equal to 18,less than or equal to 16, less than or equal to 14, less than or equalto 12, less than or equal to 10, less than or equal to 8, less than orequal to 6, less than or equal to 4, or less than or equal to 2. Otheralkyl-containing and/or aromatic-containing components are known in theart and may be used in surfactants described herein.

Various fluorophilic components can be used as the fluorophiliccontinuous phase in emulsions described herein. In some cases, thefluorophilic component of the continuous phase and the fluorophiliccomponents of the surfactant is the same. In other cases, however, theycan be different. In addition to other structures described herein, thefollowing are non-limiting examples of fluorophilic components that canbe used in either a surfactant and/or a continuous phase:perfluorodecalin, perfluoromethyldecalin, perfluoroindane,perfluorotrimethyl bicyclo[3.3.1]nonane, perfluoromethyl adamantane,perfluoro-2,2,4,4-tetra-methylpentane; 9-12C perfluoro amines, e.g.,perfluorotripropyl amine, perfluorotributyl amine,perfluoro-1-azatricyclic amines; bromofluorocarbon compounds, e.g.,perfluorooctyl bromide and perfluorooctyl dibromide; F-4-methyloctahydroquinolidizine and perfluoro ethers, including chlorinatedpolyfluorocyclic ethers, perfluoro-4-methylmorpholine,perfluorotriethylamine, perfluoro-2-ethyltetrahydrofuran,perfluoro-2-butyltetrahydrofuran, perfluoropentane,perfluoro(2-methylpentane), perfluorohexane,perfluoro-4-isopropylmorpholine, perfluorodibutyl ether,perfluoroheptane, perfluorooctane, perfluorotripropylamine,perfluorononane, perfluorotributylamine, perfluorodihexyl ether,perfluoro[2-(diethylamino)ethyl-2-(N-morpholino)ethyl]ether,n-perfluorotetradecahydrophenanthrene, and mixtures thereof. In someinstances, the fluorophilic component can be straight-chained, branched,cyclic, etc., and/or have a combination of such structures. Specificnon-limiting examples include fluoroinert PFPEs (perfluoropolyethers),such as KRYTOX®, by DuPont or perfluoropolyethers and otherfluoropolymers from Solvay Solexis.

In one particular embodiment, the choice of solvent and/or fluorophiliccomponent may include approximately matching the average chain length ofthe fluorophilic portion of the surfactant with the average chain lengthof the continuous-phase component of the mixture.

In some embodiments, surfactants have a structure such as A-B, A-B-A, or(A-B—)_(n) (i.e., A-B-A-B-A-B-A . . . ) or B-(A)_(n), or A-B-A′, oranother multi-block configuration, where A (and A′, if present)comprises a fluorophilic component and B is the hydrophilic orlipophilic component. In some cases, the surfactant may include alinking moiety, such as A-X—B, A-X—B-A, A-X—B-A′, A-X¹—B—X²-A,A-X¹—B—X²-A′, B—X-(A)_(n)-, B-(A-X)_(n)—, B—(X-A)_(n), B—(X-A)_(n),B-(A-X)_(n), B—X¹-(A-X²)_(n), (A-X—B)_(n), (A-B—X)_(n), (A-X¹—B—X²)_(n),or the like, where “X” represents a covalent bond or a linking moiety,and X¹ and X², where present, may be the same or different. Some suchstructures may have a ratio of the molecular weights of the A:B portionsof greater than or equal to 1:1, greater than or equal to 3:1, greaterthan or equal to 6:1, greater than or equal to 9:1, greater than orequal to 10:1, greater than or equal to 12:1, greater than or equal to15:1, greater than or equal to 20:1; greater than or equal to 25:1,greater than or equal to 30:1, greater than or equal to 40:1, or greaterthan or equal to 50:1, etc. Additionally or alternatively, thestructures may have a ratio of the molecular weights of the X:B portionsof greater than or equal to 1:1, greater than or equal to 3:1, greaterthan or equal to 6:1, greater than or equal to 9:1, greater than orequal to 10:1, greater than or equal to 12:1, greater than or equal to15:1, greater than or equal to 20:1; greater than or equal to 25:1,greater than or equal to 30:1, greater than or equal to 40:1, or greaterthan or equal to 50:1, etc.

As described herein, the performance of a surfactant may also depend onthe absolute block length and on the geometry of the surfactant, whichmay be tuned by changing the block length ratio in some cases. Forexample, surfactants having a structure such as A-B, A-B-A, or(A-B—)_(n) (i.e., A-B-A-B-A-B-A . . . ), B-(A)_(n), A-B-A′, A-X—B,A-X—B-A, A-X—B-A′, A-X¹—B—X²-A, A-X¹—B—X²-A′, B—X-(A)_(n)-,B-(A-X)_(n)—, (A-X—B—)_(n), (A-B—X)_(n), (A-X¹—B—X²)_(n), etc., oranother multi-block configuration, where A (and A′, if present)comprises a fluorophilic component and B is the hydrophilic orlipophilic component, may have a ratio of the lengths of the A:Bportions of greater than or equal to 1:1, greater than or equal to 3:1,greater than or equal to 6:1, greater than or equal to 9:1, greater thanor equal to 10:1, greater than or equal to 12:1, greater than or equalto 15:1, greater than or equal to 20:1; greater than or equal to 25:1,greater than or equal to 30:1, greater than or equal to 40:1, or greaterthan or equal to 50:1, etc. In these structures, “X” represents acovalent bond or a linking moiety, and X¹ and X², where present, may bethe same or different. Additionally or alternatively, these structuresmay have a ratio of the lengths of the X:B portions of greater than orequal to 1:1, greater than or equal to 3:1, greater than or equal to6:1, greater than or equal to 9:1, greater than or equal to 10:1,greater than or equal to 12:1, greater than or equal to 15:1, greaterthan or equal to 20:1; greater than or equal to 25:1, greater than orequal to 30:1, greater than or equal to 40:1, or greater than or equalto 50:1, etc.

In some embodiments, the fluorosurfactants described herein arecharacterized by a certain overall chain length of, for example, lessthan 100 monomers, less than 80 monomers, less than 60 monomers, lessthan 40 monomers, or less than 20 monomers. Additionally oralternatively, the fluorosurfactants may have an overall chain lengthof, for example, greater than 5 monomers, greater than 7 monomers,greater than 10 monomers, greater than 30 monomers, greater than 50monomers, greater than 70 monomers, or greater than 90 monomers. Inother embodiments, fluorosurfactants of the invention include only a fewmonomers, or one monomer such as a macromonomer.

The capability to tune the compositions, lengths, molecular weights,and/or the geometry of the surfactants as described herein (which may besynthesized by forming a covalent bond between the fluorophilic andhydrophilic/lipophilic components and/or by graft polymerization, forexample) allows for the tailored stabilization of droplets according tocertain embodiments of the present invention. In some embodiments,higher ratios of fluorophilic component to hydrophilic (or lipophilic)component may be appropriate for the stabilization of very small aqueousdroplets. Lower ratios may be useful for stabilizingfluorocarbon-in-water emulsions, for example. Also, the stabilization ofdouble- and multiple emulsions is possible, in certain cases.

Increasing the size and/or length of the fluorophilic component can, insome embodiments, increase steric repulsion and/or improve long termstability of the emulsions. In some cases, if surfactant molecules ofrelatively high molecular weight and/or with relatively large headgroupsare used, the adsorption of the surfactant to the interfaces can beslowed down in some cases, which may be advantageous for dropletformation, for instance, if hydrodynamic flow focusing techniques areused. Larger surfactants of suitable geometry may include largerchemical moieties, such as poly(ethylene glycol), which can allow for aneven more efficient shielding of the interfaces against the adsorptionof biological material.

For instance, without wishing to be bound by theory, the inventorsbelieve that stabilization of droplets in a fluorophilic continuousphase involves the factors and criteria described below and herein. Asshown in the diagram illustrated in FIG. 4, surfactant molecules 202 canadsorb to a newly formed droplet interface 206 during emulsification.Desorption of free surfactant molecules 207 can leave bare patches atthe interface. The anchoring strength (i.e., a measure of thethermodynamic equilibrium of adsorption and desorption) of thesurfactant is determined by the equilibrium between surfactantadsorption and desorption. The anchoring strength is greater (e.g.,shifted to the adsorbed state) if the headgroup portion (in some cases,the polar portion) of the surfactant (e.g., portion 208 of surfactant202) is soluble in the droplet phase (e.g., discontinuous phase 210).The solubility of a surfactant in the continuous, fluorophilic phase 216can be determined, for instance, by the critical micelle concentration(CMC), above which surfactant molecules will aggregate to form micelles218. For micellar surfactant molecules, the kinetics of interfacialadsorption can be slowed down significantly in some cases, as thedissolved surfactant molecules are free to diffuse to a dropletinterface. Accordingly, the dynamics of droplet stabilization duringemulsification may be important. The dynamics rely, for example, onsurfactant diffusion to a newly formed interface. Diffusion isinfluenced by various factors, including the overall molecular weight ofthe surfactant and the CMC. Generally, all other factors being equal,smaller molecules typically will diffuse faster; furthermore, theshorter the headgroup portion of the surfactant, the higher the CMC andthe better the diffusion.

Accordingly, in designing a suitable fluorosurfactant (e.g., ablock-copolymer fluorosurfactant) for stabilizing droplets in acontinuous fluorophilic phase, a suitable fluorophilic portion of asurfactant can be chosen such that sufficient steric stabilization ofthe emulsion is provided. Stabilization relies, at least in part, on thesolubility of the outer-facing portion of the surfactant (i.e., theportion facing the continuous phase) in the fluorophilic continuousphase and on a sufficient thickness of the stabilizing layer. Long-termdroplet stabilization may be achieved by droplets that include a thicksteric stabilizing layer, e.g., a thick fluorophilic layer. Thestabilizing layer may have a thickness of, for example, at least 10Angstroms in some embodiments, or at least 20 Angstroms, at least 30Angstroms, at least 40 Angstroms, or at least 50 Angstroms. In somecases, the thickness of the fluorophilic stabilization layer may begreater than about 7 to 10 Angstroms and less than about 5,000 Angstromsor less than about 1,000 Angstroms. In some embodiments involvingemulsions comprising a fluorophilic continuous phase, long fluorophiliccomponents are favorable. The fluorophilic component of a surfactant maybe at least about 7 to 10 Angstroms in length in some embodiments, or atleast about 50 Angstroms, at least about 100 Angstroms, at least about300 Angstroms, at least about 500 Angstroms, at least about 1,000Angstroms, or at least about 5,000 Angstroms in other embodiments.

In some cases, the outer-facing portion of the surfactant (e.g., thefluorophilic portion of a surfactant in an emulsion comprising afluorophilic continuous phase) is larger, longer, and/or has a largermolecular weight than the counterpart of the headgroup portion. Thehydrophilic or lipophilic headgroup portion may be long enough to keepthe surfactant molecules anchored at the interface and to provide asufficiently densely packed hydrophilic/lipophilic layer at the innerinterface such that it is able to provide a barrier to interfacialadsorption, e.g., for biological applications. However, too long of ahydrophilic/lipophilic component may cause crowding on the innerinterface, yielding an outer interface that is insufficiently coveredwith the fluorophilic component, and hence prone to coalescence.Sufficient coverage may be characterized by the absence of bare patchesand by a brush of sufficiently extended fluorophilic molecules on theouter interface.

Moreover, the geometry of the surfactant may be important in preventingcoalescence in some cases, which may start with the formation of a smallneck connecting two droplets. Efficient surfactants that stabilize thedroplet from coalescence may destabilize the neck. The surfactantgeometry may fit the curvature of the undisturbed droplet and oppose thecurvature of the neck. As an example, as shown in FIG. 5, theouter-facing portion of the surfactant may provide steric stabilizationof two droplets against coalescence. This block may be chosen such thatit is soluble in the continuous phase. Two sterically stabilizeddroplets 230 and 234 may be able to repel each other owing to theentropically excluded volume of the surfactant layers of each dropletinterface, as shown in view 236. Two droplets 234 and 238 may be lesssterically stable due to the entropically unfavorable interactionsbetween the surfactant layers of each droplet interface, as shown inview 240. In some cases, surfactant mobility on the interface mayfacilitate the formation of a bare patch, or a fault in the stabilizinglayer, which may lead to the formation of a neck or the coalescence ofdroplets.

A suitable headgroup portion of a fluorosurfactant described herein thatis able to anchor the surfactant to an interface of the droplet may beimmiscible with the continuous phase and, in some embodiments, may besoluble in the disperse phase. Solubility in the disperse phase,however, may allow for the potential of interaction of the headgroupportion with components or compounds contained in the droplet. Thus, insome embodiments, a fluorosurfactant described herein includes anheadgroup portion that does not interact undesirably with a componentcontained in the disperse phase. For certain biological applications,for example, PEG has been found to efficiently suppress interactions ofbiomolecules and cells with interfaces. Being water soluble andnon-toxic, PEG may be a suitable choice for an headgroup component of asurfactant in certain biological systems. Additionally, being chemicallyinert and soluble in certain organic solvents makes PEG attractive forperforming certain organic chemistry processes inside droplets. Ofcourse, other compositions such as those described herein can also beused as headgroup portions of fluorosurfactants of the invention. Anon-limiting example of such a composition is a morpholinophosphate. Inaddition, in some cases, compounds may be adsorbed onto an inner surfaceor interface, which may prevent or reduce the adsorption of biologicalcompounds, e.g., through coacervation processes. As an example, BSA maybe used as an interfacially active compound for screening residualuncovered patches.

In some embodiments, fluorosurfactants of the invention comprise twooligomeric (or polymeric) components including a fluorophilic component(e.g., component “A”) and a hydrophilic component (e.g., component “B”).These components may form a diblock-copolymer (e.g., a “A-B” structure),or other structures including those described herein. In order tosynthesize a fluorosurfactant including these components, an appropriatesolvent/solvent mixture may be chosen so as to dissolve (or at leastpartially dissolve or stabilize) both fluorophilic and hydrophilic (orlipophilic) components to provide mobility, which may be required forthe coupling reaction. In one embodiment, the fluorophilic componentcomprises a perfluorinated oligomer or polymer, such as poly(perfluoropropyleneoxide) (e.g., KRYTOX® by DuPont); the hydrophilic component mayinclude a non-fluorinated oligomer or polymer, such as poly(ethyleneglycol) (PEG). In some embodiments, 40:60 mixtures by volume offluorophilic component, e.g., methyl nonafluoroisobutylether and/ormethyl nonafluorobutylether (e.g., HFE 7100), and a solvent, e.g., THF,may be adequate to dissolve both components. In another embodiment, a1:1 mixture of a fluorophilic component, e.g., methylnonafluoroisobutylether and/or methyl nonafluorobutylether (e.g., HFE7100), and a solvent, e.g., dichloromethane, may be adequate to dissolveboth components.

Those of ordinary skill in the art can choose suitable solvents todissolve or stabilize particular components used to synthesizefluorosurfactants described herein based on, for example, knownsolubility properties of the components or by simple experimentation incombination with description provided herein. For instance, solubilityparameters (e.g., Hildebrand parameters), as described in Barton,Handbook of Solubility Parameters, CRC Press, 1983, may be used todetermine the likelihood of solubility of one component in another.Typically, chemical components having similar values of solubilityparameter are soluble in one another. Those of ordinary skill in the artcan also choose an appropriate solvent by, e.g., knowing thefluorophilic and hydrophilic (or lipophilic) components and thelikelihood of reactivity between the surfactant components and thesolvent, and/or by a simple screening test. One simple screening testmay include adding the surfactant components to the solvent anddetermining whether the surfactant components react with and/or arenegatively effected by the solvent. A screening test for choosingappropriate surfactant components and solvent for the formation of anemulsion can include mixing the components to form the emulsion andvarying either the material composition, quantities, and/orconcentration of one component while keeping the others constant, anddetermining the stability of the emulsion. The surfactants may havedifferent relative block lengths or geometries. Other simple tests canbe identified and conducted by those of ordinary skill in the art withthe benefit of the present disclosure.

In some embodiments, it is desirable to choose a particular solvent tobe contained inside droplets such as those described herein. Forexample, in some embodiments, emulsion droplets may be used as separatecompartments for particle synthesis or high throughput screening, or theparticles can be employed as miniaturized reaction sites, as describedin more detail below. Prerequisites of such use include, for example,control over the droplet size, compatibility of the components containedin the disperse phase with the disperse phase and with thefluorosurfactants, and compatibility between the disperse phase,fluorosurfactants, and the continuous phase. While droplets may be madeusing emulsification techniques in some conventional emulsion systems(e.g., hydrocarbon oil-in-water emulsions and water-in-hydrocarbon oilemulsions), chemical compatibility in these systems can be limited ifcertain solvents, such as solvents that are miscible with hydrocarbonsand water, are used as the continuous phase. In some cases, for chemicalcompatibility, the dispersed phase and the continuous phase in variousembodiments of the instant invention may be chosen to be immiscible, andthus, the solvent to be compartmentalized in droplets may be chosen tobe immiscible in the continuous phase (e.g., oil or water). For example,it may be difficult to form emulsions comprising certain alcohols orother solvents (e.g., THF) as the disperse phase, as alcohols or othersolvents may be miscible with either water or certain organic oils,e.g., mineral oils or silicon oils that are used as the continuousphase. However, using emulsions involving a fluorocarbon phase andfluorosurfactants as described herein can allow generation of emulsionscontaining a wide variety of solvents. In particular, the inventors havediscovered that emulsions of solvent droplets in fluorocarbon oils suchas those described herein can include a wide range of common solventssuch as alcohols as a discontinuous phase, which may not be possible inconventional emulsion systems. This is because fluorocarbons are at thesame time hydrophobic and lipophobic, and may thus be immiscible withalcohols.

The choice of size and geometry of a surfactant (including outer andheadgroup components) as applied to the stabilization of emulsionsincluding an alcohol as a discontinuous phase is one example oftailoring droplets using description contained herein. Without wishingto be bound by any theory, the inventors have discovered the followingtrends and observations. In order of decreasing polarity, methanol(MeOH), ethanol (EtOH), and i-propanol (i-PrOH) are similar in theirchemical properties and each does not dissolve in certain fluorocarbonoils. In some cases, each of methanol, ethanol, and i-propanol dissolvein a substance that can be used as an headgroup component of afluorosurfactant. In one embodiment, the substance is PEG or aderivative thereof, which suggests that PEG-fluorophilic (e.g.,PFPE)-block copolymers can stabilize emulsions comprising the alcoholsin a fluorophilic continuous phase. However, surprisingly, it wasdiscovered that the fairly polar methanol group may be stabilized withany of the applied surfactants, Table 1 shows that surfactants ofcertain block lengths provided long-term stabilizing i-propanolemulsions. These observations may be applied to other emulsionsincluding low polarity solvents as the discontinuous phase.

Surfactants with small PEG- and small PFPE-blocks may decrease thesurface tension; however, they may not provide colloidal stabilizationof the emulsion. Increasing the length of both the PEG- and thePFPE-blocks may improve the long-term stability of the emulsion. In somecases, the influence of the outer-facing portion of the surfactant(e.g., PFPE) may be more important for long term stabilization than thatof the headgroup portion (e.g., PEG). This suggests that the failure ofemulsion stabilization may be dominated by the formation of a bare patchon the interface of two adjacent droplets, giving rise to neck formationand subsequent coalescence. This may also suggest that an inappropriatesurfactant geometry or too short of an headgroup portion of a surfactant(e.g., PEG) that will facilitate surfactant desorption may becounterbalanced by a thicker stabilizing (e.g., outer-facing portion)layer, such as longer fluorophilic components of a surfactant.

TABLE 1 Comparison of the stability of methanol, ethanol andiso-propanol emulsions as a function of the block lengths of the appliedsurfactant 3 hours after emulsification: 0220 0420 0620 0920 Cyt 0232-10232-2 0432 0632 0932 0265-1 0265-2 0465 0665 0965 MeOH E E E E S E E EE E E E E E E EtOH T E E E S T E E E E T T E E E i-PrOH S S S E E T T EE E E E E E E

Table 1 shows a summary of the effects of solvent polarity of thesolvents MeOH>EtOH>i-PrOH, listed from highest to lowest polarity,surfactant geometry and absolute chain lengths on emulsion forming andstabilization. The block-copolymers are labeled with a four-digit code,and the co-polymers can also be labeled with E2K (difunctionalpolyethylene glycol coupled to two PFPE blocks). The first two digits inthe entries in Table 1 indicate the molecular weight of the PEG blockdivided by 100, the third and fourth digit indicate the molecular weightof the PFPE block divided by 100. For example: 0220 (or E2K 0220) is asurfactant including PEG having a molecular weight of 200 g/mol and aPFPE block having a molecular weight of 2000 g/mol. The notations are asfollows: “E”—stable emulsion was formed; “T”—slightly less stableemulsion that “E”; “S”—least stable emulsion was formed. “Cyt” isCytonix FluorN surfactant, commercially available from Cytonix.

As the difference in polarity of the disperse and continuous phasesbecomes smaller, larger PEG-blocks and/or larger PFPE-blocks may berequired for stabilizing emulsions. Larger PEG-blocks may provide abetter anchoring strength to the interface compared to smallerPEG-blocks. Larger PFPE-blocks may shield a greater interfacial areamore efficiently against coalescence compared to smaller PFPE-blocks. Insome cases, the effect of the PFPE-block variation is more pronouncedthan that of the PEG-block variation. This may be due to the capabilityof a greater stabilizing moiety to cover a nearby bare patch or preventor inhibit the bare patch from forming. In some embodiments, an increasein the size of one or both of the blocks could decrease the surfactantmobility on the interface, making the formation of bare patches lesslikely.

In another embodiment, an emulsion of the present invention comprisesTHF as a discontinuous phase and a fluorophilic continuous phasestabilized by fluorosurfactants described herein. In one embodiment, thesurfactant comprises PEG and PFPE. In some cases, both longer PEG andlonger PFPE blocks may afford an improved stabilization; the effect ofthe PFPE blocks may be more pronounced. In other cases, however, thereare exceptions to this trend. For instance, surfactants including a PEGportion that has a higher molecular weight than the PFPE portion maystabilize droplets better than surfactants including a PFPE portion thathas a higher molecular weight that the PEG portion. This result may beassociated with the pronounced geometry of the surfactant molecules thatcause the formation of thermodynamically stable, swollen micelles thatcannot coalesce.

In certain embodiments, fluorosurfactants of the invention includetriblock-copolymers (e.g., A-B-A structures), whose mid-block is solublein the discontinuous phase. This “double-tail” morphology is known tohave advantages in the colloidal stabilization properties over certain“single-tail” (e.g., A-B) surfactants. In some embodiments, themid-block can include a poly(ethylene glycol) moiety. Many poly(ethyleneglycol)s are available with two reactive headgroups on either end of thepolymer-chain, which can facilitate the synthesis of double-tailmorphologies. However, the synthetic routes described herein may be usedfor the synthesis of other surface active morphologies, such asdiblock-copolymers, multi-block-copolymers, polymer brushes, etc. Insome cases, the triblock copolymer may also contain one or more linkingmoieties, for example, as in the structure (A-X¹—B—X²)_(n), where each“X” independently represents a covalent bond or a linking moiety, andthe each X may be the same or different.

The following example syntheses use poly(ethylene glycol) as thehydrophilic component of a headgroup; however, the synthesis can beapplied to the formation of surfactants including other chemicalmoieties. In particular, the synthetic routes described herein can beeasily applied to the coupling of a variety of other hydrophiliccomponents.

In some embodiments, surfactants including poly(ethylene glycol) as thehydrophilic component of a headgroup are advantageous for performingchemical and/or biological reactions (e.g., enzymatic reactions andreactions involving cells and/or cellular components). Poly(ethyleneglycol)s are well known and widely applied to “passivate” surfacesagainst non-specific adsorption of nucleic acids and proteins to solidsurfaces. (Harris, J. M.; Zalipsky, S. on Poly(ethylene glycol):Chemistry and Biological Applications, American Chemical Society,Washington, D.C.; 1997). For the same reason, poly(ethylene glycol)surfactants such as Tween (Bernath, K.; Hai, M.; Mastrobattista, E.;Griffiths, A. D. Magdassi, S.; Tawfik D. S. in Analytical Biochemistry,325: 151-157; 2004) and Triton (Mastrobattista, E.; Taly, V.; Chanudet,E.; Treacy, P.; Kelly, B. T.; Griffiths, A. D. in Chemistry & Biology,12: 1291-1300; 2005) have been applied for in vitro compartmentalizationin hydrocarbon oils.

In some instances, a fluorophilic component and a non-fluorophiliccomponent (e.g., a hydrophilic or lipophilic component) of a surfactantare bonded covalently. However, in other embodiments, ionic bonds orother associations, such as linking moieties, can be used to combine thetwo components. Non-limiting examples of reactions for coupling two ormore components together follows.

Three different, non-limiting coupling reactions are now described,which can be used to achieve coupling of the fluorophilic andhydrophilic components. These include the formation of an ester bond, anamide bond, or an ether bond between a hydrophilic and fluorophiliccomponent. The chemicals used in the synthetic routes described hereinare produced on the industrial scale and therefore readily available.

While the amide bond may be formed in a particularly simple reaction of,e.g., poly(ethylene glycol) diamine, the formation of ether bonds mayinvolve the use of hydroxyl terminated poly(ethylene glycol) components,which are inexpensive and are available in a wide variety of chainlengths. In some instances, ether bonds are more stable to hydrolysisthan esters or amides; thus they may allow for a wider range ofapplicable pH.

In one embodiment, an ester bond may be formed through the reaction of,for example, poly(ethylene glycol) dicarboxylic acid withthionylchloride to yield the poly(ethylene glycol) diacid chloride, withwhich a fluoropolymer with a terminal alcohol group may react in thepresence of poly(vinyl pyridine). The inverse case of reacting thefluorophilic acid halide with the poly(ethylene glycol) dialcohol(PEG(OH)₂) is possible as well.

In another embodiment, an amide bond may be formed through simpleamidation reaction. For example, a poly(ethylene glycol) or othercomponent comprising a mono- or diamine reacts on a fluoropoymercarrying a terminal methylester to yield the amide may be used. Theformation of the inverse amide is possible as well.

In another embodiment, an ether bond may be synthesized using aMitsunobu reaction, which links, for example, two components havinghydroxyl functional groups. For instance a fluoropolymer and apoly(ethylene glycol) may both comprise hydroxyl functional groups andcan be bonded using a Mitsunobu reaction. DEAD (diethylazodicarboxylate) and triphenyl phosphine may be used for activating theless acidic poly(ethylene glycol) alcohol. Sorbitol may be applied as anoptional hydrophilic group. Williamson ether synthesis is also possiblewith certain hydrophilic headgroups. A Williamson ether synthesis mayalso be used for linking a fluorophilic and lipophilic component. Forinstance, a tosylated fluoropolymer can be linked to an organic alcoholin the presence of an organic base.

Other synthetic routes may involve very reactive species, such asisocyanates (forming urethane bonds), or precursors that are amphiphilesby themselves, such as fluorocarbons with acid, nitrile or acidhalogenide headgroups that may be coupled to the hydrophilic componentyielding esters and amides. Various reagents may be used to activatecarboxylic groups (e.g. BOP).

The details of some of these synthetic routes are described below, butare intended to be exemplary only and not limiting. Possible ways topurify the products are indicated in these procedures as well. Aparticularly interesting method of purification includes phaseseparation of the unreacted fluorophobic reactant from an appropriatelow-polarity fluorosolvent mixture. The unreacted fluorophobic compoundwill cream, forming a supernatant that may be easily decanted. At thesame time, block-copolymer surfactant may phase separate if the criticalmicelle concentration is exceeded, but it will sediment, rather thancream, due to the high density of the fluorocarbon components containedin the surfactant molecules.

In one particular embodiment, suitable geometries and acceptablestabilization of droplets in fluorocarbon oils have been achieved usingthe ether synthesized from the reaction of phytol and KRYTOX® alcoholwith a molecular weight of 1,700 g/mol. The molecular weight ratio inthis example was about 1:6. A molecular weight ratio of poly(ethyleneglycol) to poly(perfluoropropylene oxide) of 1:4 to 1:5 was suitable forthe stabilization of THF droplets in fluorocarbon oils. The appliedpoly(ethylene glycol) contained 75% diamine and 25% of monoamine,yielding 75% triblock and 25% diblock co-polymer.

In some embodiments, unreacted mixtures of the methyl ester ofKRYTOX®-fluoropolymers and poly(ethylene glycol) diamines may reduce thesurface tension between water and fluorocarbon oils and stabilizedroplets. Therefore, interfacially active emulsifying systems that relyon the interaction of appropriately functionalized fluoropolymers withamines and polyethers across the interface are contemplated within thescope of the present invention, even if the fluorophilic and thehydrophilic (or lipophilic) components are not bound covalently.Similarly, the application of poly(ethylene glycol) and amines to screenthe interface of droplets that are stabilized with conventionalsurfactant systems are contemplated within the scope of the presentinvention.

In one embodiment, a fluorosurfactant of the invention has theappropriate geometry for suitably stabilizing (e.g., sterically)droplets of hydrocarbon oils and organic solvents in fluorocarbon oils.In some cases, a fluorosurfactant includes lipophilic headgroups forstabilizing inverse emulsions that comprise hydrocarbon oils and organicsolvents in addition to water. Also in these cases, thefluorosurfactants may comprise oligomeric or polymeric fluorocarbontails, which can allow long term colloidal stability againstcoalescence. This may be achieved, for instance, through sufficientsteric repulsion.

The surfactant syntheses described herein include, but are not limitedto, coupling a perfluorinated component to a lipophilic component in asuitable solvent mixture. As a fluorophilic component, a perfluorinatedoligo- or polymer, such as an poly(perfluoro propyleneoxide) (e.g.KRYTOX® by DuPont), was used. The lipophilic component can be anotheroligomeric component, such as poly(ethylene glycol), poly(propyleneglycol) or poly(ethylene-co-butylene), poly-THF, or an alkyl componentsuch as lauryl or phytol. Other examples include, but are not limitedto, proteins, or aromatics. This may represent a convenient route tosurfactants of low to intermediate chain lengths with a well definedstructure and molecular weight distribution. Other suitable methods ofsynthesis are known to those of ordinary skill in the art. The solventused for the coupling reaction may be chosen to dissolve both componentsto provide their mobility required for the coupling reaction. 40:60mixtures by volume of methyl nonafluorobutyl ether (3M's HFE 7100) andTHF showed good results in some experiments. Other non-limiting examplesof suitable solvents include HFE 7100 (3M) and dichloromethane orfluorochlorocarbons.

Another aspect of the invention includes stabilizing emulsions involvingelectrostatic attraction of two oppositely charged components (e.g., afirst surfactant including a headgroup and a tail, and a secondsurfactant including a headgroup and a tail), one of which is soluble inthe dispersed phase, the other soluble in the continuous phase. The twocomponents may combine to form at the interface between the continuousand discontinuous phases to stabilize an emulsion. The component solublein the continuous phase may include an ionic surfactant suitable forstabilizing inverse emulsions. The component soluble in the dispersephase may assemble as a layer of counterions to the surfactantheadgroups at the interface. Particularly suited are counterionscarrying multiple charges as they cannot be replaced easily by othercharged species. They may be chosen to fit the desired surface chemistrythat allows for chemical/biochemical/biological reactions inside thedroplets.

As a non-limiting example of such a system,poly(perfluoropropyleneoxide) carboxylic acid (KRYTOX® FS series) wasdissolved in a continuous fluorous phase and a polycation was dissolvedin the dispersed phase. Polycations may carry functionalities such asprimary, secondary, tertiary, or quaternary amines. In some experiments,0.01%-0.5% (w/w of the aqueous phase) low molecular weight chitosan(Aldrich) were dissolved in the aqueous phase. The precise weightfractions of each component will depend on, for example, the dropletsize and on the cationic charge density. For chitosan, both the primaryamine and the quaternary ammonium salt may be suitable for preventingthe adsorption of biomolecules to the interfaces.

To produce stable droplets of organic solvents 0.01%-0.5% (w/w),polymeric ammonium salts with counterions which are highly soluble inthe organic phase and inert to chemical reactions were added. Suitablepolycations include, for example, poly-N-methyl-vinylpirydinium,quaternized poly-N-vinyl-imdazole, polyallylamine, or LUVIQUAT® (BASF).Other polycations are known in the art and can also be used. Suitablecounter-anions include 4-(trifluoromethyl)-benzenesulfonate, ortrifluoromethanesulfonate. Other counter-anions are known in the art andcan also be used.

In another embodiment, two surfactants can be dissolved in a continuousfluorous phase and combined to assemble at the interface between thecontinuous and discontinuous phase of an emulsion. One surfactant canprovides colloidal stability of the emulsion. For example, KRYTOX® 157FSL can be used for steric stabilization of the droplets. The othersurfactant can be chosen to prevent adsorption of components such aschemicals, reactants, and biomolecules to the interfaces. For example,small amounts (<0.5% by weight) of a commercial fluorous surfactant thatcomprises a poly(ethylene glycol) group, such as ZONYL® (DuPont) FSN,may be used to sterically block the charges of the KRYTOX® surfactant.

The emulsions of the present invention may be formed using any suitableemulsification procedure known to those of ordinary skill in the art. Inthis regard, it will be appreciated that the emulsions can be formedusing microfluidic systems, ultrasound, high pressure homogenization,shaking, stirring, spray processes, membrane techniques, or any otherappropriate method. In one particular embodiment, a micro-capillary or amicrofluidic device is used to form an emulsion. The size and stabilityof the droplets produced by this method may vary depending on, forexample, capillary tip diameter, fluid velocity, viscosity ratio of thecontinuous and discontinuous phases, and interfacial tension of the twophases.

Non-limiting examples of microfluidic systems potentially suitable foruse with the instant invention include the following, each incorporatedherein by reference: U.S. patent application Ser. No. 11/024,228, filedDec. 28, 2004, entitled “Method and Apparatus for Fluid Dispersion,” byStone, et al., published as U.S. Patent Application Publication No.2005/0172476 on Aug. 11, 2005; U.S. patent application Ser. No.11/246,911, filed Oct. 7, 2005, entitled “Formation and Control ofFluidic Species,” by Link, et al., published as U.S. Patent ApplicationPublication No. 2006/0163385 on Jul. 27, 2006; U.S. patent applicationSer. No. 11/360,845, filed Feb. 23, 2006, entitled “Electronic Controlof Fluidic Species,” by Link, et al., published as U.S. PatentApplication Publication No. 2007/0003442 on Jan. 4, 2007; andInternational Patent Application No. PCT/US2006/007772, filed Mar. 3,2006, entitled “Method and Apparatus for Forming Multiple Emulsions,” byWeitz, et al., published as WO 2006/096571 on Sep. 14, 2006.

In some embodiments, an emulsion may be formed by mixing an aqueous orhydrocarbon component with the fluorocarbon component, the mixturehaving a water or hydrocarbon content of between about 1-40%, in somecases between about 5-25%, and in other cases between about 10-15%. Inanother embodiment, the emulsion has a water or hydrocarbon content ofat least about 20%, at least about 30%, at least about 40%, or at leastabout 50%, or at least 80%, etc. However, certain embodiments of theinvention provide an emulsion within reverse emulsion droplets having adisperse aqueous or lipophilic phase in a continuous, fluorocarbonphase. The criteria in accordance with certain embodiments of theinvention that can be used to select suitable discontinuous phases,continuous phases, and surfactants suitable for use in the invention mayinclude (but are not limited to) the description contained herein. Asimple, non-limiting screening test to determine whether an aqueous (orhydrocarbon)-in-fluorocarbon emulsion has been created follows: If awater-soluble, fluorocarbon-insoluble dye is added to an emulsion, ifthe emulsion is an aqueous-in-fluorocarbon emulsion the dye may form aseparate phase, since it is not miscible with the continuous,fluorocarbon phase. But in the case of a fluorocarbon-in-aqueousemulsion, the dye may dissolve in the continuous, aqueous phase givingthe appearance of disillusion of the dye in the entire mixture. In asecond non-limiting screening test, the aqueous phase can be madeslightly electrically conductive and, if the emulsion is slightlyelectrically conductive, then the continuous phase is aqueous, i.e. afluorocarbon-in-aqueous phase results. If the mixture is notelectrically conductive, then an aqueous-in-fluorocarbon emulsionresults. As a third non-limiting screening test, if the mixture isoptically clear, then very small aqueous aggregates in a fluorocarbon,continuous phase may have been formed.

In one embodiment, emulsions of the invention are prepared usingmicrofluidic systems. For instance, the formation of droplets atintersection 92 of device 90 is shown in FIG. 6. As shown inillustrative embodiment, fluid 94 flows in channel 96 in the directionof arrow 98. Fluid 94 may be, for example, an aqueous or lipophilicsolution that forms the discontinuous phase of a droplet. Fluid 104flows in channel 106 in the direction of arrow 107, and fluid 108 flowsin channel 110 in the direction of arrow 112. In this particularembodiment, fluids 104 and 108 have the same chemical composition andserve as a carrier fluid 116, which is immiscible with fluid 94. Inother embodiments, however, fluids 104 and 108 can have differentchemical compositions and/or miscibilities relative to each other and tofluid 94. At intersection 92, droplet 120 is formed by hydrodynamicfocusing after passing through nozzle 122. These droplets are carried(or flowed) in channel 124 in the direction of arrow 126.

Droplets of varying sizes and volumes may be generated within themicrofluidic system. These sizes and volumes can vary depending onfactors such as fluid viscosities, infusion rates, and nozzlesize/configuration. Droplets may be chosen to have different volumesdepending on the particular application. For example, droplets can havevolumes of less than 1 μL (microliter), less than 0.1 μL (microliter),less than 10 nL, less than 1 nL, less than 0.1 nL, or less than 10 pL.

Emulsions including a fluorophilic continuous phase may be useful in avariety of fields due to their unique properties, according to anotheraspect of the invention. For example, one or more of the followingadvantages may be present in certain emulsions of the invention. Afluorophilic continuous phase may be immiscible with water andhydrocarbons and may allow separation of both hydrophilic and lipophiliccompounds that can be contained within the droplets. In this way,cross-contamination of materials, such as proteins or DNA, betweendroplets may be reduced or prevented. This efficientcompartmentalization can be advantageous for drop-based biologicaland/or chemical assays and the like. In addition, fluorophilic solventssuch as fluorocarbons may be chemically inert. Their immiscibility withcommon organic solvents allows for making droplets or organic solventsthat may be used as reactors with volumes typically on the order ofpicoliters, in certain embodiments of the present invention. In someembodiments, these emulsions can provide the dry environment that isnecessary for carrying out water-sensitive chemical reactions. Certainfluorophilic solvents may also have a solubility for gases and can allowtransport of gaseous compounds to and from the droplets. For example,biological experiments carried out with cells inside the droplets maybenefit from the enhanced transport of oxygen. Microfluidic experimentsmay also be performed in polydimethylsiloxane (PDMS) or other polymericdevices obtained through the widely applied methods of soft-lithography.For instance, in contrast to mineral and silicone oils, certainfluorophilic solvents such as perfluorinated oils do not swell therubbers and avoid a number of problems associated therewith.

Accordingly, the droplets and emulsions produced in accordance withvarious embodiments of the present invention have a variety of uses. Forexample, in one embodiment, the droplets are used as reaction vesselsfor carrying out chemical and/or biological reactions within thedroplet. Increasing effort is being put into investigating biologicalsystems on very small scales. This involves the observation of cells andtheir interaction with the environment as well as the investigation ofstrands of DNA, even of single genes. There are certain advantages tothe encapsulation of cells and DNA into aqueous droplets (e.g., adispersed phase of an emulsion) that are separated from one another withoil (e.g., a continuous phase), as is discussed herein. This is calledcompartmentalization and it generally allows the screening of muchlarger numbers of cells or genes at greater rates using much lesschemicals than in classical experimental setups, such as Petri-dishes ormicrotiter plates.

As mentioned above, fluorocarbon oils may be suited as the continuousphase in some of these experiments, as they may reducecross-contamination, e.g., through the diffusion of hydrophilic orlipophilic biological material from one droplet to another. Furthermore,they may allow for an efficient transport of oxygen in some cases, whichis vital to some types of encapsulated cells.

In some applications, a role of the fluorosurfactant may be to ensurecolloidal stability of the emulsion upon collision of droplets and/orduring incubation in a creamed state. The surfactant may also reduce orprevent biological molecules from adsorbing to the interface of thedroplet, which adsorption could disturb their native three-dimensionalstructure or render them inactive. For example, PEG and other headgroupsdescribed herein may reduce or prevent adsorption of certain biologicalmolecules to interfaces and hence may be used for these applications. Infact, a model reaction for the in-vitro translation and transcription ofspecific DNA sequences into fluorescent proteins inside emulsiondroplets demonstrates the potential of various fluorosurfactants of theinvention (e.g., non-ionic fluorosurfactants) for biological in-vitroexperiments.

In some embodiments, such as certain bioapplications that involveincubation at elevated temperatures, fluorosurfactants of the inventionmay comprise a water soluble fluorosurfactant such as the Zonylcompounds sold by DuPont. Some such compounds have relatively longPEG-units (400 g/mol and greater) and a short fluorotelomer. Thecompounds may be added to the water phase, but in some cases, they maybe added to the fluorophilic phase. Such compounds can, in someembodiments, help keep biomolecules, such as BSA, from adsorbing to thedroplet interface. They may aid the emulsification process and may alsohelp in stabilizing the droplets during emulsification in some cases.

In other embodiments, a high-molecular weight surfactant may be insertedinto the adsorbed surfactant layer after emulsification. Thehigh-molecular weight surfactant may increase long term stabilization ofthe emulsion. In some cases, such a surfactant can be mixed with afluorosurfactant before dissolving it in the fluorophilic continuousphase. Alternatively, the surfactant can be added to the fluorophiliccontinuous phase separately or added after emulsification of anemulsion.

In some embodiments, in-vitro translation can be performed usingemulsions described herein. A gene (e.g., a DNA sequence) can becontained in the droplets together with all the chemicals required fortranscribing it into RNA and translating that into a protein. Suchchemicals are known to those of ordinary skill in the art, and may bereadily obtained commercially. This protein may be fluorescent itself(e.g., green fluorescent protein, GFP) or enzymatically active,catalyzing a reaction that yields a fluorescent product. A fluorescentproduct may not be formed if adsorption to the interfaces of one of thecompounds takes place, disturbing the 3D-structure of the bioactivecompound and rendering it inactive. Fluorescence indicates that thereactions took place and, therefore, that adsorption had been preventedsuccessfully. This is demonstrated in the right-most vessel of anexample as shown in FIG. 7. The negative control, the left-most vesselof FIG. 7, shows only background fluorescence. The emulsion used in thisparticular experimental example included a fluorophilic continuous phase(FC 40) and an aqueous solution with an in-vitro translation mix andZonyl, and the surfactant E2K 0420.

In certain embodiments, the discontinuous aqueous and/or lipophilicphase of a droplet/emulsion may include one or more physiologicallyacceptable reagents. The reagents may be dissolved or suspended in thediscontinuous phase. In another set of embodiments, the discontinuousaqueous and/or lipophilic phase of a droplet/emulsion may include one ormore reagents that can participate in a chemical and/or in a biologicalreaction of interest. Non-limiting examples of reagents that can beinvolved in a chemical and/or biological reaction, or other chemicaland/or biological process, include: buffers, salts, nutrients,therapeutic agents, drugs, hormones, antibodies, analgesics,anticoagulants, anti-inflammatory compounds, antimicrobial compositions,cytokines, growth factors, interferons, lipids, oligonucleotidespolymers, polysaccharides, polypeptides, protease inhibitors, cells,nucleic acids, RNA, DNA, vasoconstrictors or vasodilators, vitamins,minerals, stabilizers and the like. In other embodiments, thediscontinuous aqueous and/or lipophilic phase can contain toxins and/orother substances to be tested, assayed, or reacted within the droplet.Accordingly, chemical and/or biological reactions may be performedwithin droplets of the invention. Because conditions of pH, temperature,reactant concentration, and the like will be adjusted for a particularreaction that is to take place within the disperse phase of theemulsion, in some cases, the surfactant system may be tailored so as topreserve the emulsion under these conditions.

As specific examples, in one embodiment, a therapeutic agent can beprovided in the aqueous phase of a droplet and a reactant introducedinto the aqueous phase, optionally via a carrier or by fusion ofdroplets, and allowed to react inside the droplet. In anotherembodiment, droplets of the invention can be used as drug-deliverycarriers.

The invention also provides, according to another aspect, a techniquefor controlling the length of assembly of components within droplets.For instance, for polymerization reactions within a droplet, the size ofthe resulting particle can be controlled by confining the space withinwhich the reaction can occur. The confined space may be defined by thesize of the droplets, which can serve as microreactors in some cases.For example, when a polymeric precursor is provided in the discontinuousphase and a reactant is added to the discontinuous phase, the reactantmay be allowed to interact with the precursor and cause polymerization,according to certain embodiments. Because of the size of the dropletsand the limited amount of discontinuous phase, polymer particle size maybe accordingly limited. Smaller particles than the precursor dropletsmay be prepared, for instance, by diluting the polymer precursor withappropriate solvents. In one particular embodiment, such a reaction caninvolve the polymerization of monomer units to form polyurethane.

Confining chemical reactions in small volumes is of interest for variousreasons. For example, combinatorial approaches to chemical synthesisrequire that a large number of reactions be performed with slightlydifferent compositions or under systematically changed conditionswithout using large amounts of chemicals. By screening the resultingproducts, as discussed herein, optimal reaction conditions can be foundor scaled up to commercial scales. The droplets may also serve assuitable containers in some cases. 2) Certain products and intermediatesare worth more if they are available as micron or nanometer sizedobjects (e.g., in lattices). These products span the range of, forexample, micron-sized heterogeneous catalysts, crystalline nanoparticleswith controlled electronic and photonic properties, polymericdispersions, fillers used for nanocomposite materials, etc. One way toachieve such confined reactions is to carry them out in the droplets ofan emulsion. Emulsions usually include the oil- or solvent phase and acontinuous water phase. However, many organic reactions are sensitive towater and an aqueous continuous phase may not be used. Using afluorophilic continuous phase (e.g., fluorocarbon oils) instead of wateras the continuous phase for such systems, as described herein, may beused to circumvent this problem. In some cases, appropriate surfactantsmay also be added, e.g., to increase stability of the emulsion.

In one particular embodiment, the methods and components describedherein can be used to stabilize droplets of organic solvents forcombinatorial chemistry. Choosing a suitable combination of inner (e.g.,lipophilic/hydrophilic) and outer (e.g., fluorophilic) components mayallow for the stabilization of droplets of organic solvents, as requiredfor performing many water-sensitive chemical reactions. For instance,this allows for the facilitated combinatorial screening of chemicalreactions by using microfluidic devices. Note that the surfactantscontaining, e.g., poly(ethylene glycol) as the discontinuous phase asdescribed herein, also can allow stabilization of droplets of a varietyof organic solvents (e.g., THF and acetone).

In another embodiment, the methods and components described herein canbe used for nanoparticle synthesis. Droplets of organic solvents may bestabilized (as the discontinuous phase) for the production of organicand inorganic micron or sub-micron particles. This makes the synthesisof particles formed from water-sensitive precursors possible, e.g.,polyurethanes and polyesters. In another embodiment, crystalline silicaand titania particles may be synthesized in water-free reactions. Theabsence of water, in certain embodiments, offers advantages over sol-gelmethods, which may be used to yield entirely amorphous particles.

In one embodiment, particle synthesis can be achieved in a suspensionpolymerization process in which a liquid precursor is emulsified andthen each of the emulsion droplets is converted, e.g., 1:1, yielding apolymer particle. Suspension polymerization is an industrially importantmethod that can form particles with sizes ranging from less than amicron to tens of microns, for example. The suspension polymerizationprocess can be used with a variety of chemical compositions. Suspensionpolymerization, in some cases, relies on phase separation (and/orchemical compatibility) between the precursor and the continuousemulsion phase.

Non-limiting examples of other materials that can be synthesized usingmethods described herein include silica, titania, vanadia, zirconia,etc., and combinations thereof, for instance, by sol-gel reactions, toform particles or the like. These and other reactions may be performed,for instance, acid or base-catalyzed. For example, base-catalyzedreactions may yield nanoparticles through nucleation and growth insidethe droplets, according to some embodiments. In some cases, thenanoparticles may adhere to one another after solvent evaporation.

In one embodiment, a suitable continuous emulsion phase for polyurethane(PU) suspension polymerization may be perfluorinated oils, as these oilsphase may separate from the hydrocarbon-based PU precursors, and may bewater-free in some cases. Certain fluorosurfactants of the invention canachieve stabilization of PU droplets, as described herein. Examples ofthe synthesis of stabilized polyurethane particles and emulsions aredescribed in more detail in the Examples section.

In some embodiments, polyurethanes or other polymer or polymerprecursors within a dispersed phase may be modified by adding reagents,such as linking moieties, to the precursor that will be incorporatedinto the polymer backbone in the course of polymerization. In somecases, the composition of the precursor droplets is the same or similarto that of the precursor before emulsification and does not rely on thediffusion of precursors. This can make suspension polymerization moreversatile than techniques such as emulsion or precipitationpolymerization according to some embodiments. As another example, stepgrowth polymerization reactions, including the polyaddition ofpolyurethanes, may be used. Such reactions can involve homogeneousdistribution of added reagents along the polymer chains. In someembodiments, this approach is used to incorporate fluorescent dyes inthe polyurethane, e.g., through urea links. Other compounds can also beincorporated using this approach.

An example is illustrated in FIG. 10A. This figure is a bright fieldmicrograph of dried, fluorescently labeled, monodisperse particles of apolyurethane latex. The synthesis of fluorescent particles is just oneexample of chemical modification through the addition of functionalreagents to the PU-precursor. FIG. 10B is a similar view, showing afluorescent micrograph of the particles.

In another embodiment, cross-linked particles (e.g., cross-linkedpolyurethane particles) can be formed. Cross-linking may be possible,for example, by replacing a small amount of dialcohol or diisocyanatewith a trifunctional reagent, while maintaining a generallystochiometric 1:1 ratio of alcohol and isocyanate groups. Suspensionpolymerization can produce cross-linked particles in a singlepolymerization step, in some embodiments. Additionally, if desired,fluorescent labeling may not require an additional processing step. Insome embodiments involving the surfactant systems described herein,neither cross-linker molecules nor reactive dyes may significantlychange the colloidal stability of these emulsions. Effectivecross-linking can be shown by dissolution tests with an appropriatesolvent, such as THF. The example as shown in FIG. 11A illustrates howthat upon application of THF, cross-linked particles may swell in somecases, but do not appear to dissolve as readily as would particles thatare not as well cross-linked.

Certain cross-linked polymer particles synthesized in this way may nothave gradients in the cross-linking density. Accordingly, a polymernetwork having homogeneously distributed cross-links may be produced insome embodiments. In some cases, homogeneously distributed cross-linkscan be formed using the step polymerization mechanism. Cross-linked,monodisperse, and fluorescently labeled organic microgel particles areshown in the example of FIG. 11B. Such particles may be useful as modelsystems in fundamental studies.

In some embodiments, various mechanical properties of the polymerparticle can be tuned by reducing the effective volume fraction of theprecursor within a particle. This may be achieved, for example, bydiluting the precursor with an inert solvent that can dissolve theprecursor as well as the polymer. In this way, suspension polymerizationcan allow control over the mesh size of a cross-linked polymer particle.Particles (e.g., microgel particles) that were polymerized with smallvolume fractions of precursor may swell upon addition of a suitablesolvent. Depending on the degree of swelling, such particles can exhibitdifferent stiffnesses or other physical properties. For instance, FIGS.12A and 12B show examples of cross-linked PU-particles, whose precursorwas diluted with an equal volume of DMSO prior to emulsification in thiscase. The dried particles may shrink as indicated by the pronouncedwrinkles at their surface (or comparison, FIG. 9B shows cross-linkedparticles of the same composition that were synthesized from anundiluted PU-precursor).

In some embodiments, particles formed by methods such as those describedherein may be used as scaffolds for adding additional coatings orfeatures to the particles. For instance, particles may serve asscaffolds for composite particles; for example, the particle network maybe swollen with a precursor of another polymer that is polymerizedsubsequently. The synthesis of such particles can benefit from theability to stabilize organic droplets in a wide range of polarities,including DMSO, with PEG-based non-ionic fluorosurfactants, or othersurfactants described herein.

In some cases, porous structures can be formed using methods describedherein. For example, mesoporous structures may be formed inside adroplet through templated synthesis (e.g. through self assembly ofblock-copolymers). As described herein, fluorosurfactants includingnon-ionic fluorosurfactants can be used in a wide range of particlesyntheses through conversion of precursor emulsion droplets. Theimmiscibility of fluorocarbon oils with hydrocarbons of many differentpolarities may allow the formation of droplets having certainhydrocarbon disperse phases that cannot be formed in certain othercontinuous phases. In addition, hydrophobic chemicals may be emulsifiedin a dry environment allowing water-sensitive reactions to be performed.While the benefits of such a system has been demonstrated in conjunctionwith the suspension polymerization of polyurethane particles, it shouldbe understood that the invention is not limited in this respect and thatarticles and methods described herein can be used to form particleshaving other compositions in other embodiments. Furthermore, in a simpleone-step process, solid particles can be made with the option ofcross-linking, grafting fluorescent dyes or other moieties to thepolymer network and controlling its mesh-size by applying an inertsolvent during polymerization. This process may be used for producing avariety of other polymers that rely on water-sensitive syntheses, suchas, for example, polyesters and polyureas, and for producing transitionmetal alkoxides. Organic droplets that allow for water sensitivereactions are useful in fields other than particle synthesis, such asheterogeneous catalysis or screening applications in drop-basedmicrofluidics. In some instances, methods and components describedherein can be used for reactions with gases. For example, reactions ofliquids with gaseous reactants (such as hydrogenations and oxidationsusing hydrogen and oxygen, respectively) may be carried out veryefficiently. Fluorocarbon oils can dissolve around an order of magnitudemore gases than water and conventional solvents in some cases. The highgas solubility and the large interfacial area of emulsions comprising afluorophilic continuous phase may enhance the transport of the gaseousreactant(s) to the reaction loci inside the droplets, which often is therate limiting step in industrial processes. Transport across theinterface can be facilitated by the enormous specific area of emulsiondroplets. Thus, articles and methods described herein can be used forchemical heterophase reactions. Applications of water-sensitivecatalysts are also possible.

In another embodiment, methods and components described herein can beused for studies of liquid crystalline behavior. Lyophilic mesophases offluorocarbon surfactants are interesting because of their particularcontrast in hydrophilicity. The synthetic routes described herein may beapplied for the production of such materials.

In another embodiment, methods and components described herein can beused for modifying the wetting behavior of microchannels. Chemicals usedas wetting agents are typically chemically inert and capable of changingthe wetting properties of fluorous and silicone elastomers in areversible manner. By adsorbing them onto a solid-liquid interface, theyprovide a surface that changes the wetting behavior in a reversiblemanner. For instance, silicone rubbers may be wet by fluorocarbon oilsand fluorous rubbers may be wet by hydrocarbon oils and organicsolvents.

In certain embodiments, colloidal stabilization of droplets can beachieved while preventing the adsorption of biological materials. Forinstance, using passivating agents such as PEGs as headgroups ofsurfactants, droplets containing solutions of biomolecules may bestabilized in fluorocarbon oils while preventing the adsorption of DNA,RNA, proteins or other materials to the interfaces. In some embodiments,cells may be encapsulated in aqueous droplets without adsorbing to thedroplet interfaces. They may therefore be investigated as if they werefloating in an aqueous bulk medium.

Some embodiments of the invention involve mixtures of more than onedifferent surfactant. The combination of surfactants synthesized usingmethods described herein with similar or different geometry anddifferent molecular weight allows for efficient emulsification. Forinstance, low molecular weight surfactants may lower the interfacialtension rapidly, while high molecular weight surfactants may providelong term stability. Such considerations are crucial to the velocity ofan emulsification process, e.g., in industry.

The methods and components described herein can also be used for studiesof liquid crystalline behavior. For example, lyophilic mesophases offluorocarbon surfactants are interesting because of their large contrastin hydrophilicity. The synthetic routes described herein may be appliedfor the production of such materials, e.g., as previously discussed.

In some embodiments, surfactants having the following structures arecontemplated:

1. PFPE (KRYTOX®)-PEG-PFPE (KRYTOX®), where PFPE is perfluoropolyether:F—[CF(CF3)CF₂O]_(x)—CF(CF₃)CONH—(CH₂CH₂O)_(y)CH₂CH₂—NHCOCF(CF₃)—[OCF₂CF(CF3)]_(x)—Fwith various chain lengths, for example:

KRYTOX ® block: M_(W) = 1950 g/mol corresponds to x = 10.7 KRYTOX ®block: M_(W) = 4,000 g/mol corresponds to x = 23.0 KRYTOX ® block: M_(W)= 8,000 g/mol corresponds to x = 47.1 PEG block: M_(W) = 400 g/molcorresponds to y = 7.7 PEG block: M_(W) = 1,000 g/mol corresponds to y =21.82. PFPE (KRYTOX®)-PolyTHF-PFPE (KRYTOX®), where PFPE isperfluoropolyether:F—[CF(CF3)CF₂O]_(x)—CF(CF₃)CONH—(CH₂CH₂CH₂CH₂O)_(y)CH₂CH₂CH₂CH₂—NHCOCF(CF₃)—[OCF₂CF(CF3)]_(x)-F

KRYTOX ® block: M_(W) = 1950 g/mol corresponds to x = 10.7 KRYTOX ®block: M_(W) = 4,000 g/mol corresponds to x = 23.0 PTHF block: M_(n) =350 g/mol corresponds to y = 3.9 PTHF block: M_(n) = 1100 g/molcorresponds to y = 14.93. PFPE—alkyls:F—[CF(CF3)CF₂O]_(n)—CF(CF₃)CONH—(CH₂)_(n)—H

KRYTOX ® block: M_(W) = 1950 g/mol corresponds to n = 10.74. Phytol may be used in some cases. Phytol is a branched C₁₈hydrocarbon block that may be linked with an ether bond:(CH₃)₂HC—(CH₂)₃CH(CH₃)—(CH₂)₃CH(CH₃)—(CH₂)₃C(CH₃)═CH—O—CH₂CF(CF₃)—[OCF₂CF(CF₃)_(n)]—F

KRYTOX ® block: M_(W) = 1950 g/mol corresponds to n = 10.75. PFPE—sugars:For example, sorbitol can be linked to KRYTOX® with an ether bond:H—[CH(OH)]₅—CH₂—O—CH₂CF(CF₃)—[OCF₂CF(CF3)]_(n)—F

KRYTOX ® block: M_(W) = 1950 g/mol corresponds to n = 10.76. Glucosamine is a glucose derivative that may be linked to KRYTOX®with an amide bond:glucose-NHCOCF(CF₃)—[OCF₂CF(CF3)]_(n)-F

KRYTOX ® block: M_(W) = 1950 g/mol corresponds to n = 10.7Glucose is a 6 membered heterocycle of the sum formula C₆O₆H₁₂, in whichthe first and the fifth carbon atom are linked to the oxygen atom of thering. Glucosamine carries an amine group instead of the OH-group at thesecond carbon atom.

The following documents are incorporated herein by reference in theirentirety: U.S. Provisional Patent Application Ser. No. 60/392,195, filedJun. 28, 2002, entitled “Multiphase Microfluidic System and Method,” byStone, et al.; U.S. Provisional Patent Application Ser. No. 60/424,042,filed Nov. 5, 2002, entitled “Method and Apparatus for FluidDispersion,” by Link, et al.; U.S. Provisional Patent Application Ser.No. 60/461,954, filed Apr. 10, 2003, entitled “Formation and Control ofFluidic Species,” by Link, et al.; U.S. Provisional Patent ApplicationSer. No. 60/498,091, filed Aug. 27, 2003, entitled “Electronic Controlof Fluidic Species,” by Link, et al.; U.S. patent application Ser. No.08/131,841, filed Oct. 4, 1993, entitled “Formation of MicrostampedPatterns on Surfaces and Derivative Articles,” by Kumar, et al., nowU.S. Pat. No. 5,512,131, issued Apr. 30, 1996; International PatentApplication No. PCT/US96/03073, filed Mar. 1, 1996, entitled“Microcontact Printing on Surfaces and Derivative Articles,” byWhitesides, et al., published as WO 96/29629 on Jun. 26, 1996; U.S.patent application Ser. No. 09/004,583, filed Jan. 8, 1998, entitled“Method of Forming Articles Including Waveguides via CapillaryMicromolding and Microtransfer Molding,” by Kim, et al., now U.S. Pat.No. 6,355,198, issued Mar. 12, 2002; International Patent ApplicationNo. PCT/US01/17246, filed May 25, 2001, entitled “Patterning of SurfacesUtilizing Microfluidic Stamps Including Three-Dimensionally ArrayedChannel Networks,” by Anderson, et al., published as Publication No. WO01/89788 on Nov. 29, 2001; International Patent Application No.PCT/US01/46181, filed May 25, 2001, entitled “Methods and Compositionsfor Encapsulating Active Agents,” by Weitz, et al., published asPublication No. WO 02/47665 on Jun. 20, 2002; International PatentApplication No. PCT/US02/23462, filed Jul. 24, 2002, entitled “LaminarMixing Apparatus and Methods,” by Stroock, et al., published as WO03/011443 on Feb. 13, 2003; and International Patent Application No.PCT/US03/20542, filed Jun. 30, 2003, entitled “Method and Apparatus forFluid Dispersion,” by Stone, et al., published as Publication No. WO2004/002627 on Jan. 8, 2004. Also incorporated herein by reference isU.S. patent application Ser. No. 11/246,911, filed Oct. 7, 2005,entitled “Formation and Control of Fluidic Species,” by Link, et al.;U.S. patent application Ser. No. 11/024,228, filed Dec. 28, 2004,entitled “Method and Apparatus for Fluid Dispersion,” by Stone, et al.;International Patent Application No. PCT/US2006/007772, filed Mar. 3,2006, entitled “Method and Apparatus for Forming Multiple Emulsions,” byWeitz, et al.; and U.S. patent application Ser. No. 11/360,845, filedFeb. 23, 2006, entitled “Electronic Control of Fluidic Species,” byLink, et al.

The following applications are each incorporated herein by reference:U.S. Provisional Patent Application Ser. No. 60/659,045, filed Mar. 4,2005, by Weitz, et al.; U.S. Provisional Patent Application Ser. No.60/498,091, filed Aug. 27, 2003, by Link, et al.; U.S. ProvisionalPatent Application Ser. No. 60/392,195, filed Jun. 28, 2002, by Stone,et al.; U.S. Provisional Patent Application Ser. No. 60/424,042, filedNov. 5, 2002, by Link, et al.; U.S. Pat. No. 5,512,131, issued Apr. 30,1996 to Kumar, et al.; International Patent Publication WO 96/29629,published Jun. 26, 1996 by Whitesides, et al.; U.S. Pat. No. 6,355,198,issued Mar. 12, 2002 to Kim, et al.; International Patent ApplicationSerial No.: PCT/US01/16973, filed May 25, 2001 by Anderson, et al.,published as WO 01/89787 on Nov. 29, 2001; International PatentApplication Serial No. PCT/US03/20542, filed Jun. 30, 2003 by Stone, etal., published as WO 2004/002627 on Jan. 8, 2004; International PatentApplication Serial No. PCT/US2004/010903, filed Apr. 9, 2004 by Link, etal.; U.S. Provisional Patent Application Ser. No. 60/461,954, filed Apr.10, 2003, by Link, et al.; International Patent Application Serial No.PCT/US2004/027912, filed Aug. 27, 2004, by Link, et al.; U.S.Provisional Patent Application Ser. No. 60/659,046, filed Mar. 4, 2005,entitled “Systems and Methods of Forming Particles,” by Garstecki, etal.; and a U.S. utility patent application, entitled “Systems andMethods of Forming Particles,” by Garstecki, et al., filed on even dateherewith.

The following examples are intended to illustrate certain embodiments ofthe present invention, but are not to be construed as limiting and donot exemplify the full scope of the invention.

EXAMPLE 1

The following is an example of a procedure for forming an amide bondbetween a headgroup and a fluorophilic component of a surfactant:

Chemicals:

-   -   PEG-diamine (M_(w)=400 from Tomah)    -   KRYTOX® methylester (KRYTOX®-COOMe) (M_(w)=1900)    -   THF (dry) or CH₂Cl₂ (dry)    -   HFE 7100 (added molecular sieve to ensure dryness)    -   possibly molecular sieves for drying    -   for purification (removal of excess KRYTOX®-COOMe):        Aminomethylstyrene-crosslinked        Materials:    -   stirrer    -   distillation setup, or a rotavap    -   flasks (100 ml), stirrers and standard equipment like glass        syringes (Pyrex), funnel, etc.        Procedure:    -   1.) Dissolve 0.5 g of PEG-diamine (400 g/mol) (Tomah) in 15 ml        THF. Use a 50 ml or 100 ml flask.    -   2.) Dissolve 4.69 g KRYTOX®methylester (1,900 g/mol, corresponds        to 10% excess considering the presence of 25% PEG-monoamine in        the Tomah product) in 10 ml HFE 7100.    -   3.) Mix the solutions from 1.) and 2.) and stir at room        temperature overnight (or up to several days) in a tightly        sealed flask. Do not heat.    -   4.) Suggestion for purification: If a greater excess of        KRYTOX®-COOMe is applied, Aminomethylstyrene may be used to        remove it. Add a 10 fold excess with respect to the excess of        KRYTOX®-COOMe and stir overnight. Filter off and rinse with a        60:40 mixture by volume of THF:HFE 7100.        -   Secondly, precipitation of the surfactant in a suitable            solvent mixture may be used for removing unreacted            PEG-reactant. Unreacted PEG phase-separates and can cream,            dragging along some of the solvent. This phase can be easily            decanted.        -   At the same time, the can surfactant phase-separate to form            a fluffy precipitate in the lower, fluorocarbon-rich phase.            This may be due to the low solubility of the PEG-blocks in            the solvent mixture.    -   5.) Evaporate the solvent mixture not exceeding a temperature of        40° C. (Rotavap).        Remarks:    -   One alternative solvent: 1:1 mixture of CH₂Cl₂ and HFE 7100.    -   Other block lengths of the PEG and the KRYTOX®-block have been        applied. One good combination seems to be Tomah PEG-diamine (400        g/mol) and KRYTOX® methylester (4,000 g/mol). In all of these        experiments the stochiometric ratio was kept constant. Reaction        times were increased with increasing chain length and were        varied at room temperature from one day to one week.

EXAMPLE 2

This example illustrates the following procedure for forming an esterbond between a headgroup and a fluorophilic component of a surfactant:

Chemicals:

-   -   PEG—dicarboxylic acid (M_(w)=600, from Sigma-Aldrich)    -   KRYTOX® Alcohol (Mw=1900)    -   SOCl₂    -   4-Polyvinylpyridine (2% cross-linked, from Sigma-Aldrich)    -   DMF (dry, as a catalyst, however: only small amount)    -   CH₂Cl₂ (best if dry—Sure Seal bottle or DrySolv)    -   THF (dry)    -   HFE 7100    -   possibly molecular sieves for drying        Materials:    -   hot plate stirrer with external temperature probe    -   oil bath    -   reflux setup with balloon    -   glass filter/column with silica/glass wool    -   distillation setup—or ideally a rotavap, balance    -   flasks (100 ml), stirrers and standard equipment like glass        syringes (Pyrex), funnel, etc.        Procedure:    -   1) Dissolve 1 g dicarboxy-PEG in 10 ml methylenechloride.        Helpful: Use a 100 ml flask.    -   2) Add 0.8 g (0.6 ml) thionylchloride (corresponds to 2-fold        excess), while cooling the flask on ice. Don't use plastic        syringes.    -   3) Add approximately 15 drops of dimethylformamide as a catalyst        from a 20 gauge needle.    -   4) Take to room temperature and let react for half an hour, then        heat to 36° C. and let react overnight. Put a reflux column to        the flask, the top of it was closed with a balloon (H₂O        sensitive compounds, HCl-formation).    -   5) Evaporate methylenechloride, thionylchloride and DMF        (distillation, best with rotavap). Try not to exceed 40° C., as        this may produce unexpected reactions and color changes due to        SOCl₂. Keep under vacuum for 2 hours to make sure everything has        evaporated.    -   6) Add 6 ml THF to the PEG acid chloride (tune viscosity).    -   7) Add 0.85 g Polyvinylpyridine (2-fold excess) for        neutralization, stir well.    -   8) Add 9.5 g KRYTOX® alcohol (about a 1.5-fold excess) dissolved        in a mixture of 12 ml THF and 12 ml HFE 7100 under cooling in an        ice-bath.    -   Remark: This is a rough minimum of the amount of solvent needed.        At room temperature, there will be two phases, but at 50° C. the        upper THF phase will dissolve. For more solvent, add a 60:40%        v/v mixture of THF:HFE 7100.    -   9) Stir vigorously for 30 minutes at room temperature (in order        to disperse the solid polyvinylpyridine well). Then heat up to        about 56-60° C. and let react overnight. It may include a reflux        column with a balloon on top.    -   10) After cooling down, filtrate over a glass filter funnel or a        bed of 2 cm silica. Use a 60:40 mixture of THF and HFE 7100 for        washing, the polyvinylpyridine and the filter. Filtration can be        done after 1 day, but not much may came off upon washing in some        cases.    -   11) Further purification: evaporate solvent. A precipitate of        the fluoro-compound(s) may be formed by increasing the        THF-concentration.

EXAMPLE 3

For testing emulsion stabilities of the emulsions shown in Table 1, theemulsions were formulated containing Fluorinert Electronic Liquid FC 40fluorocarbon oil (available from 3M) with 1.6 wt % of the respectivefluorosurfactant. FC 40 is a perfluoro compound with primarily compoundswith 12 carbons, with the hydrogen replace by F. 10% v/v with respect tothe fluorocarbon phase and the alcohol was added. Emulsification wascarried out by first turning over the vessel, then shaking it by handfor 15 s and finally shaking it vigorously by hitting the edge of atable for an additional 15 s and for an additional minute, ifemulsification was insufficient.

EXAMPLE 4

This example describes the synthesis of polyurethane particles usingarticles and methods described herein, according to one embodiment ofthe invention. In this example, the emulsions were formed by shaking theprecursor and a fluorocarbon oil in the presence of fluorosurfactant.

Polyurethane latexes were synthesized from a stochiometric ratio ofpolyethylene glycol (a dialcohol) of a molecular weight of about 200g/mol with hexanediisocyanate to form urethane bonds. This wasemulsified in a fluorocarbon phase comprising the oil FC 40 and 1.6 wt %of the surfactant E2K 0420.

Emulsification of the polyurethane precursor yielded separate dropletswith a similar chemical composition as the precursor liquid. Crudeemulsions were obtained by shaking up the precursor and a fluorocarbonoil in the presence of fluorosurfactant, yielding a polydisperseprecursor emulsion.

The resulting rubbery polymer resembled soft blocks of Spandex. At highdegrees of polymerization, the liquid precursor became solid. Therefore,the mechanical properties of the product was used as a measure ofconversion.

One way to confirm that the use of a continuous fluorocarbon phaseresults in a high degrees of polymerization or solid particles is byremoving the continuous fluorocarbon phase through evaporation. Onlysolid particles have the mechanical rigidity to resist coalescence andretain their spherical shape in spite of capillary forces. This wastested with a crude polydisperse precursor emulsion obtained by shaking.FIG. 8A shows a bright field micrograph of such an emulsion afterpartial conversion; it displays both patches of coalesced droplets andsolid particles upon drying.

An additional probe for conversion is the presence of fluorescein, afluorescent dye added to the reaction mixture prior to emulsification.Fluorescein is quenched in the presence of isocyanates and does notfluoresce. Fluorescence reappears, however, as the isocyanate is used upin the course of the reaction. Cross-polarization microscopy (FIG. 8B)shows the low conversion of the coalesced patches by the absence offluorescence, and the higher conversion of the un-coalesced particles byits presence. The presence of solid particles indicates that thefluorosurfactants may be suited for stabilizing polyurethane precursoremulsions in fluorocarbon oils in some cases. Moreover, it demonstratesthe benefits of this water-free emulsion system by maintaining agenerally stochiometric ratio of water-sensitive isocyanate and alcoholmoieties. This confirms that there were, at best, very low levels ofwater present that could degrade the isocyanate precursor. In this case,if water was present, the stochiometric ratio of the reagents would beshifted and conversions would remain too low to yield solid particleswith the applied precursors. Hence, this example demonstrates thatorganic droplets in fluorocarbon oils may be stable. Such emulsions canprovide a water-free system that may allow a wide range of organicsynthetic reactions to be performed inside droplets that representveritable mini-reactors.

EXAMPLE 5

This example describes the synthesis of polyurethane particles usingarticles and methods as described herein in various embodiments of thepresent invention. In this example, the emulsions were formed using flowfocusing techniques.

Polyurethane latexes were synthesized from a generally stochiometricratio of polyethylene glycol (a dialcohol) of a molecular weight of 200g/mol with hexanediisocyanate to form urethane bonds. This wasemulsified in a fluorocarbon phase comprising the oil FC 40 and 1.6 wt %of the surfactant E2K 0420.

Emulsions with control over the droplet size were obtained byhydrodynamic flow focusing in microfluidic devices. For the rapidprototyping of such devices, soft lithography was used to form devicesin polydimethylsiloxane (PDMS). Monodisperse emulsion droplets wereformed when co-flowing streams of the continuous and of the precursorphase were forced into one microfluidic output channel. Surface tensioncaused the disperse stream to break up into discrete droplets. Asurfactant that is dissolved in the continuous phase adsorbed to thenewly formed interfaces of the droplets, thereby stabilizing thedroplets against coalescence.

FIG. 9A shows a monodisperse PU-precursor emulsion in fluorocarbon oil.Its polymerization yields monodisperse particles (FIG. 9B). Upon drying,the fully converted particles exhibited small wrinkles on theirsurfaces. However, these wrinkles may be due to particle deformations onthe glass slide that arose from the low glass transition temperature ofthe polymer, and can be prevented by using other substrates.

These results demonstrate that control over the particle size ispossible by combining microfluidic emulsification with suspensionpolymerization. Moreover, it shows that the applied surfactant allowedfor emulsification through hydrodynamic flow focusing and that itstabilized the fluorocarbon based emulsions sufficiently againstcoalescence throughout the polymerization and even at elevatedtemperature.

EXAMPLE 6

FIG. 13A shows reinjection of aqueous droplets into a microfluidicdevice containing 3% BSA and 0.1% Zonyl FSN with respect to water. Thecontinuous phase was FC 40, the surfactant E2K 0420 (100 mg E2K 0420added to 3 ml FC 40, which was equivalent to about 1.6%).

FIG. 13B shows the same system as described in FIG. 13A, illustratingcollection (before reinjection) of the droplets. The droplets wereobserved to be somewhat deformed. However the droplets did not coalesce,which is an indication of the stability of the droplets.

FIG. 14 shows the same system as described in FIG. 13A and illustratesthe formation of droplets by hydrodynamic flow focusing. The dropletswere stabilized immediately after emulsification so that they would notcoalesce. The droplets came into contact immediately after theirformation, but did not coalesce, which suggests that rapid diffusion ofthe fluorosurfactants to the newly formed interfaces had occurred.

FIG. 15 shows monodisperse droplets formed in microfluidic devicescontaining viable yeast cells. This example shows that monodispersedroplets may be formed with a E2K 0420 surfactant.

EXAMPLE 7

This example illustrates the synthesis of certain surfactants of thepresent invention, specifically AEH12, AEH14, AEH19, AEH22, AEH23,AEH100, AEH101, AEH102, AEH103, AEH104, AEH105, AEH106, or AEH107.

The perfluoroether and Krytox FS(H) were purchased from Dupont. The PEGwas PEG monomethoxy with a molar mass of 750 g/mol (purchased fromSigma-Aldrich). All other chemicals were purchased from Sigma-Aldrich.

Thin-layer chromatography (TLC) analyses were performed on RP-18 silicagel F-254 plates (Merck). Silica gel (70-230 mesh, Merck) was used forcolumn chromatography.

Synthesis of AEH12 head group. 3.14 g of 2-phenylethanol (20.45 mmol)and 7.1 ml of triethylamine (2.5 eq) were dissolved in 50 ml of drytetrahydrofuran (THF) and added dropwise, at 0° C. and under anhydrousnitrogen, to 3.14 g of phosphorus oxytrichloride (20.45 mmol) in 100 mlof THF. The mixture was stirred at 0° C. for 3 hours. A solution of 3.56g morpholine (40.90 mmol) and 14.2 ml triethylamine (2.5 eq) in 50 ml ofTHF was then added dropwise to the stirred reaction mixture, which wasmaintained free of oxygen and cooled with an ice-bath. After stirringfor 18 hours the mixture was allowed to warm to room temperature,triethylamine hydrochloride was filtered off, and the solvent and excessof amine were removed under vacuum. The clear oily residue was driedunder reduced pressure and purified by chromatography (ethylacetate/methanol 9:1). The yield of this reaction was 70%(P,P-dimorpholino P-(2-phenylethyloxyd) phosphate). Purity wasdetermined by TLC (R_(f) value: 0.7, ethyl acetate/methanol 9:1).

Synthesis of other head groups. The same procedure was applied for thesynthesis of the other head groups, substituting with the appropriatecomponents where necessary. Following synthesis, the structures of someof the head groups were verified by ¹H nuclear magnetic resonance (NMR).NMR spectra for AEH12, AEH14, and AEH19 were collected using a Bruker AC400 spectrometer and are shown in FIGS. 16A-16C.

Preparation of the acyl chloride of Krytox FS(H). The acyl chloride ofKrytox FS(H) was prepared by adding an excess of thionyl chloride (4equivalents) under an anhydrous atmosphere and vigorously mixing for 1hour. After this time, the excess of thionyl chloride was removed undervacuum.

Grafting the acyl chloride of Krytox FS(H) to the P,P-dimorpholinoP-(2-phenylethyloxyd) phosphate. The acyl chloride of Krytox FS(H) tailwas grafted to the P,P-dimorpholino P-(2-phenylethyloxyd) phosphate headgroup using a Friedel-Craft reaction. A solution of 0.78 g of theP,P-dimorpholino P-(2-phenylethyloxyd) phosphate head group (0.68 mmol)and 0.11 g (1.2 eq) of aluminium trichloride were mixed in 50 ml of THFand stirred under reflux for 1 hour. Then, under vigorous agitation,2.27 g of the acyl chloride of Krytox FS(H) was then added and thereaction mixture was stirred under reflux overnight.

The THF was removed under vacuum by rotary evaporation. The residualwhite viscous mixture was resuspended in Fluorinert Electronic LiquidFC-3283 and filtered on Celite 545. The celite was washed with 200 ml ofFC-3283 to recover all of the surfactant. The filtrate was thendistilled under vacuum by rotary evaporation to remove the FC-3283 andrecover the final product: AEH12.

Grafting the acyl chloride of Krytox FS(H) to the other head groups. Thesame procedure was applied for the synthesis of all the othersurfactants, substituting with the appropriate components wherenecessary.

Characterization of the surfactants: Emulsion stability. Water-in-oil(w/o) emulsions were generated in a microfluidics device (a“droplet-former”) using a flow-focusing geometry to form the droplets.An aqueous stream was infused from one channel through a narrowconstriction with oil streams on either side hydrodynamically-focusingthe water stream. Different combinations of flow rates and/or devicegeometries generated steady streams of uniform droplets of water in oilwith volumes in the range of 10-500 pl.

The oil phase in each experiment was formed from the fluorocarbon oilFluorinert Electronic Liquid FC-40 (manufactured by 3M) containing thedissolved surfactant of interest. The aqueous phase wasphosphate-buffered saline (PBS).

To determine the stability of each emulsion, the emulsion was collectedin a Hamilton glass syringe and then reloaded into the droplet-formingdevice using the same oil phase to space out the droplets. An emulsionwas considered stable in this example if more than 99% of the dropletswere not coalesced on reloading.

Results. The following surfactants generated stable w/o emulsions usingthe methodology described above when the surfactant concentration was inthe range 0.5-2.5% (w/w): AEH12, AE14, and AEH19. The other surfactantswere not tested in this example.

Compatibility with mammalian cells. 100 microliters of FC-40 oilcontaining a surfactant of interest were pipetted into the well of aclear 96-well plate. 100 microliters of a cell suspension containing1.5×10⁴ cells in Dulbecco's Modified Eagle's Medium supplemented with10% (v/v) fetal bovine serum were then layered on top of the oil in eachwell. The cells were detached human HEK 293T expressing greenfluorescent protein (GFP). After 24 hours the cells were examined bybright-field and fluorescence microscopy.

After 24 hours, bright-field microscopy revealed that the cells seededdirectly on the well bottom (a control), on FC-40 alone, and on FC-40containing AEH12 were healthy (FIGS. 17A-17H). The cells seeded on FC-40containing the non-biocompatible surfactant R22 (Raindance Technologies)were unhealthy and appeared lysed. Fluorescence microscopy, revealingthe distribution of intact GFP-containing cells, supported theseobservations. In FIG. 17, FIGS. 17A to 17D are bright-field microscopeimages of HEK 293T cells on the following surfaces: (17A) the bottom ofa plastic well (control); (17B) FC-40 oil; (17C) FC-40 oil containing2.5% (w/w) AEH12; and (17D) FC-40 oil containing 2.5% (w/w) R22. FIGS.17E to 17H are fluorescence microscope images of the same samples.

Compatibility with in vitro transcription-translation. An in vitrotranscription-translation reaction was prepared by adding 5 nM of “T7promoter-evolved β-galactosidase (EBG) Class IV-T7 terminator” DNAfragments and 500 micromolar fluorescein di-β-D-galactopyranoside (FDG)to a Novagen EcoPro T7 transcription-translation reaction (EMDBiosciences). A control reaction containing no DNA fragments wasprepared as well. Each reaction was emulsified in FC-40 containing 2.5%(w/w) AEH19 using a droplet-forming device. The droplets generated ineach case were 10 pl in volume. Each emulsion was collected andincubated at 30° C. for 1.5 hours and then reloaded into thedroplet-forming device. Several thousand droplets from each emulsionwere stimulated with 488 nm-wavelength laser light and their emissionsin the fluorescein channel were measured.

After 1.5 hours at 30° C. it was observed that the droplets containingthe EBG Class IV genes exhibited much greater fluorescence than dropletscontaining no genes per droplet (FIG. 18). This figure shows histogramsof emissions in the fluorescein channel for populations of dropletscontaining transcription-translation reactions. The grey histogramcorresponds to the droplets containing EBG Class IV genes. The blackhistogram corresponds to the droplets containing no genes. It wasconcluded that the fluorescent signal of the former population wasincreased due to the presence of the genes; thus, the genes inside thedroplets were transcribed and translated, resulting in the production ofan enzyme (EBG Class IV) that was able to cleave the non-fluorescentsubstrate FDG, releasing fluorescent fluorescein.

Compatibility with purified enzymes. An enzymatic reaction containingthe following components was prepared: 50 mM Tris HCl pH 8, 10 mMcalcium chloride, 10 mM ethylamine, 200 micromolar phenazinemethosulphate (PMS), 100 micromolar resazurin, 10 micromolarpyrroloquinoline quinone (PQQ), and alcohol dehydrogenase (ADH) proteinin 0.05% (v/v) ethanol. For each surfactant, 200 microliters of thisaqueous solution were emulsified in 200 microliters of FC-40 containingthe surfactant of interest by vigorously shaking for 1 minute. 50microliters of each emulsion was transferred to the well of a black96-well plate. Every 4 seconds, the wells of the plate were stimulatedwith 540 nm-wavelength light and the resulting emissions at 590nm-wavelength were measured.

The enzymatic reaction described above should generate fluorescentresorufin by reducing the non-fluorescent resazurin when the ADH isactive. The reaction profiles for the different surfactants revealedthat emulsification of the reaction using the surfactants AEH12, AEH14,and AEH19 was not detrimental to its progress (FIG. 19). Conversely,emulsification of the reaction using the non-biocompatible surfactantR22 appeared to significantly reduced the rate of the reaction.

While several embodiments of the present invention have been describedand illustrated herein, those of ordinary skill in the art will readilyenvision a variety of other means and/or structures for performing thefunctions and/or obtaining the results and/or one or more of theadvantages described herein, and each of such variations and/ormodifications is deemed to be within the scope of the present invention.More generally, those skilled in the art will readily appreciate thatall parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the teachings of thepresent invention is/are used. Those skilled in the art will recognize,or be able to ascertain using no more than routine experimentation, manyequivalents to the specific embodiments of the invention describedherein. It is, therefore, to be understood that the foregoingembodiments are presented by way of example only and that, within thescope of the appended claims and equivalents thereto, the invention maybe practiced otherwise than as specifically described and claimed. Thepresent invention is directed to each individual feature, system,article, material, kit, and/or method described herein. In addition, anycombination of two or more such features, systems, articles, materials,kits, and/or methods, if such features, systems, articles, materials,kits, and/or methods are not mutually inconsistent, is included withinthe scope of the present invention.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “comprising” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of”, when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

It should also be understood that, unless clearly indicated to thecontrary, in any methods claimed herein that include more than one stepor act, the order of the steps or acts of the method is not necessarilylimited to the order in which the steps or acts of the method arerecited.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively, as set forth in the United States Patent Office Manual ofPatent Examining Procedures, Section 2111.03.

What is claimed is:
 1. A surfactant, comprising a block copolymerincluding a perfluorinated polyether (PFPE) block coupled to apolyethylene glycol (PEG) block via an amide bond, wherein the PFPEblock comprises a formula of F(CF(CF₃)CF₂O)_(x)—CF(CF₃)CONH—, wherein xis an integer greater than or equal to 8; and the PEG block comprises aformula of—(C_(n)H_(2n) O)_(y)—or —(C_(n)H_(2n)O)_(y)—CH₃, wherein n isa positive integer and y is an integer greater than or equal to
 10. 2.The surfactant of claim 1, wherein the surfactant comprises one block ofPFPE and one block of PEG.
 3. The surfactant of claim 1, wherein thesurfactant comprises two blocks of PFPE and one block of PEG.
 4. Acomposition comprising the surfactant of claim
 1. 5. The composition ofclaim 4, further comprising a hydrophobic liquid.
 6. The composition ofclaim 4, further comprising an aqueous liquid.
 7. The composition ofclaim 4, further comprising a fluorinated oil and an aqueous liquid. 8.The composition of claim 7, wherein the aqueous liquid additionallycomprises biological molecules.
 9. The composition of claim 8, whereinthe biological molecules comprise nucleic acids.
 10. A method of formingaqueous droplets, comprising: providing a microfluidic device; providingan aqueous liquid to the microfluidic device; providing a fluorinatedliquid to the microfluidic device; providing a surfactant comprising ablock copolymer that includes a perfluorinated polyether (PFPE) blockcoupled to a polyethylene glycol (PEG) block via an amide bond, andcomprises a formula —(C_(n)F_(2n)O)_(x)—(C_(m)F_(2m))_(y)—CONH— whereinn, m, x, and y are positive integers; and forming aqueous droplets inthe fluorinated liquid in the presence of the surfactant.
 11. The methodof claim 10, wherein the microfluidic device comprises a first channelintersecting a second channel at a junction.
 12. The method of claim 11,wherein the aqueous liquid flows in the first channel and thefluorinated liquid flows in the second channel.
 13. The method of claim12, wherein the aqueous droplets are formed at the junction.
 14. Themethod of claim 13, wherein the microfluidic device includes a nozzle,and the droplets form after the aqueous and fluorinated liquids passthrough the nozzle.
 15. The method of claim 10, wherein the aqueousdroplets comprise biological molecules.
 16. The method of claim 15,wherein the biological molecules comprise nucleic acids.
 17. The methodof claim 10, wherein the aqueous droplets comprise buffers, salts,nutrients, therapeutic agents, drugs, hormones, antibodies, analgesics,anticoagulants, anti-inflammatory compounds, antimicrobial compositions,cytokines, growth factors, interferons, lipids, polymers,polysaccharides, polypeptides, protease inhibitors, cells, RNA, DNA,vasoconstrictors, vasodilators, vitamins, minerals, or stabilizers. 18.The method of claim 10, wherein the aqueous droplets comprisefluorescent molecules.
 19. The method of claim 10, wherein thesurfactant comprises the formula —(CF(CF₃)CF₂O)_(x)—CF(CF₃)CONH—,wherein x is greater than or equal to
 8. 20. A method of forming aqueousdroplets, comprising: providing a microfluidic device; providing anaqueous liquid to the microfluidic device; providing a fluorinatedliquid to the microfluidic device; providing a surfactant of claim 1,and forming aqueous droplets in the fluorinated liquid in the presenceof the surfactant.